feat: Adds React 18 and 19 migration plugin (#1339)

- Adds React 18 and 19 migration orchestration plugins
- Introduces comprehensive upgrade toolkits for migrating legacy React 16/17 and 18 codebases to React 18.3.1 and 19, respectively. Each plugin bundles specialized agents and skills for exhaustive audit, dependency management, class/component API migration, test suite transformation, and batching regression fixes.
- The React 18 toolkit targets class-component-heavy apps, ensures safe lifecycle and context transitions, resolves dependency blockers, and fully automates test migrations including Enzyme removal. The React 19 toolkit addresses breaking changes such as removal of legacy APIs, defaultProps on function components, and forwardRef, while enforcing a gated, memory-resumable migration pipeline.
- Both plugins update documentation, plugin registries, and skill references to support reliable, repeatable enterprise-scale React migrations.

docs/README.skills.md

@@ -242,6 +242,16 @@ See [CONTRIBUTING.md](../CONTRIBUTING.md#adding-skills) for guidelines on how to
 | [python-pypi-package-builder](../skills/python-pypi-package-builder/SKILL.md) | End-to-end skill for building, testing, linting, versioning, and publishing a production-grade Python library to PyPI. Covers all four build backends (setuptools+setuptools_scm, hatchling, flit, poetry), PEP 440 versioning, semantic versioning, dynamic git-tag versioning, OOP/SOLID design, type hints (PEP 484/526/544/561), Trusted Publishing (OIDC), and the full PyPA packaging flow. Use for: creating Python packages, pip-installable SDKs, CLI tools, framework plugins, pyproject.toml setup, py.typed, setuptools_scm, semver, mypy, pre-commit, GitHub Actions CI/CD, or PyPI publishing. | `references/architecture-patterns.md`<br />`references/ci-publishing.md`<br />`references/community-docs.md`<br />`references/library-patterns.md`<br />`references/pyproject-toml.md`<br />`references/release-governance.md`<br />`references/testing-quality.md`<br />`references/tooling-ruff.md`<br />`references/versioning-strategy.md`<br />`scripts/scaffold.py` |
 | [quality-playbook](../skills/quality-playbook/SKILL.md) | Explore any codebase from scratch and generate six quality artifacts: a quality constitution (QUALITY.md), spec-traced functional tests, a code review protocol with regression test generation, an integration testing protocol, a multi-model spec audit (Council of Three), and an AI bootstrap file (AGENTS.md). Includes state machine completeness analysis and missing safeguard detection. Works with any language (Python, Java, Scala, TypeScript, Go, Rust, etc.). Use this skill whenever the user asks to set up a quality playbook, generate functional tests from specifications, create a quality constitution, build testing protocols, audit code against specs, or establish a repeatable quality system for a project. Also trigger when the user mentions 'quality playbook', 'spec audit', 'Council of Three', 'fitness-to-purpose', 'coverage theater', or wants to go beyond basic test generation to build a full quality system grounded in their actual codebase. | `LICENSE.txt`<br />`references/constitution.md`<br />`references/defensive_patterns.md`<br />`references/functional_tests.md`<br />`references/review_protocols.md`<br />`references/schema_mapping.md`<br />`references/spec_audit.md`<br />`references/verification.md` |
 | [quasi-coder](../skills/quasi-coder/SKILL.md) | Expert 10x engineer skill for interpreting and implementing code from shorthand, quasi-code, and natural language descriptions. Use when collaborators provide incomplete code snippets, pseudo-code, or descriptions with potential typos or incorrect terminology. Excels at translating non-technical or semi-technical descriptions into production-quality code. | None |
+| [react-audit-grep-patterns](../skills/react-audit-grep-patterns/SKILL.md) | Provides the complete, verified grep scan command library for auditing React codebases before a React 18.3.1 or React 19 upgrade. Use this skill whenever running a migration audit - for both the react18-auditor and react19-auditor agents. Contains every grep pattern needed to find deprecated APIs, removed APIs, unsafe lifecycle methods, batching vulnerabilities, test file issues, dependency conflicts, and React 19 specific removals. Always use this skill when writing audit scan commands - do not rely on memory for grep syntax, especially for the multi-line async setState patterns which require context flags. | `references/dep-scans.md`<br />`references/react18-scans.md`<br />`references/react19-scans.md`<br />`references/test-scans.md` |
+| [react18-batching-patterns](../skills/react18-batching-patterns/SKILL.md) | Provides exact patterns for diagnosing and fixing automatic batching regressions in React 18 class components. Use this skill whenever a class component has multiple setState calls in an async method, inside setTimeout, inside a Promise .then() or .catch(), or in a native event handler. Use it before writing any flushSync call - the decision tree here prevents unnecessary flushSync overuse. Also use this skill when fixing test failures caused by intermediate state assertions that break after React 18 upgrade. | `references/batching-categories.md`<br />`references/flushSync-guide.md` |
+| [react18-dep-compatibility](../skills/react18-dep-compatibility/SKILL.md) | React 18.3.1 and React 19 dependency compatibility matrix. | `references/apollo-details.md`<br />`references/router-migration.md` |
+| [react18-enzyme-to-rtl](../skills/react18-enzyme-to-rtl/SKILL.md) | Provides exact Enzyme → React Testing Library migration patterns for React 18 upgrades. Use this skill whenever Enzyme tests need to be rewritten - shallow, mount, wrapper.find(), wrapper.simulate(), wrapper.prop(), wrapper.state(), wrapper.instance(), Enzyme configure/Adapter calls, or any test file that imports from enzyme. This skill covers the full API mapping and the philosophy shift from implementation testing to behavior testing. Always read this skill before rewriting Enzyme tests - do not translate Enzyme APIs 1:1, that produces brittle RTL tests. | `references/async-patterns.md`<br />`references/enzyme-api-map.md` |
+| [react18-legacy-context](../skills/react18-legacy-context/SKILL.md) | Provides the complete migration pattern for React legacy context API (contextTypes, childContextTypes, getChildContext) to the modern createContext API. Use this skill whenever migrating legacy context in class components - this is always a cross-file migration requiring the provider AND all consumers to be updated together. Use it before touching any contextTypes or childContextTypes code, because migrating only the provider without the consumers (or vice versa) will cause a runtime failure. Always read this skill before writing any context migration - the cross-file coordination steps here prevent the most common context migration bugs. | `references/context-file-template.md`<br />`references/multi-context.md`<br />`references/single-context.md` |
+| [react18-lifecycle-patterns](../skills/react18-lifecycle-patterns/SKILL.md) | Provides exact before/after migration patterns for the three unsafe class component lifecycle methods - componentWillMount, componentWillReceiveProps, and componentWillUpdate - targeting React 18.3.1. Use this skill whenever a class component needs its lifecycle methods migrated, when deciding between getDerivedStateFromProps vs componentDidUpdate, when adding getSnapshotBeforeUpdate, or when fixing React 18 UNSAFE_ lifecycle warnings. Always use this skill before writing any lifecycle migration code - do not guess the pattern from memory, the decision trees here prevent the most common migration mistakes. | `references/componentWillMount.md`<br />`references/componentWillReceiveProps.md`<br />`references/componentWillUpdate.md` |
+| [react18-string-refs](../skills/react18-string-refs/SKILL.md) | Provides exact migration patterns for React string refs (ref="name" + this.refs.name) to React.createRef() in class components. Use this skill whenever migrating string ref usage - including single element refs, multiple refs in a component, refs in lists, callback refs, and refs passed to child components. Always use this skill before writing any ref migration code - the multiple-refs-in-list pattern is particularly tricky and this skill prevents the most common mistakes. Use it for React 18.3.1 migration (string refs warn) and React 19 migration (string refs removed). | `references/patterns.md` |
+| [react19-concurrent-patterns](../skills/react19-concurrent-patterns/SKILL.md) | Preserve React 18 concurrent patterns and adopt React 19 APIs (useTransition, useDeferredValue, Suspense, use(), useOptimistic, Actions) during migration. | `references/react19-actions.md`<br />`references/react19-suspense.md`<br />`references/react19-use.md` |
+| [react19-source-patterns](../skills/react19-source-patterns/SKILL.md) | Reference for React 19 source-file migration patterns, including API changes, ref handling, and context updates. | `references/api-migrations.md` |
+| [react19-test-patterns](../skills/react19-test-patterns/SKILL.md) | Provides before/after patterns for migrating test files to React 19 compatibility, including act() imports, Simulate removal, and StrictMode call count changes. | None |
 | [readme-blueprint-generator](../skills/readme-blueprint-generator/SKILL.md) | Intelligent README.md generation prompt that analyzes project documentation structure and creates comprehensive repository documentation. Scans .github/copilot directory files and copilot-instructions.md to extract project information, technology stack, architecture, development workflow, coding standards, and testing approaches while generating well-structured markdown documentation with proper formatting, cross-references, and developer-focused content. | None |
 | [refactor](../skills/refactor/SKILL.md) | Surgical code refactoring to improve maintainability without changing behavior. Covers extracting functions, renaming variables, breaking down god functions, improving type safety, eliminating code smells, and applying design patterns. Less drastic than repo-rebuilder; use for gradual improvements. | None |
 | [refactor-method-complexity-reduce](../skills/refactor-method-complexity-reduce/SKILL.md) | Refactor given method `${input:methodName}` to reduce its cognitive complexity to `${input:complexityThreshold}` or below, by extracting helper methods. | None |