Remove collections folder and migrate remaining references to plugins

- Remove rug-agentic-workflow collection files (already migrated to plugin)
- Remove collections.instructions.md (no longer applicable)
- Remove suggest-awesome-github-copilot-collections prompt and plugin command
- Update awesome-copilot plugin.json to reference skills prompt instead of collections
- Update contributor-report.mjs to track plugins instead of collections
- Remove unused collection constants from constants.mjs
- Update rug-agentic-workflow plugin.json with tags and items from collection
- Regenerate README docs and marketplace.json

docs/README.plugins.md

@@ -16,7 +16,7 @@ Curated plugins of related prompts, agents, and skills organized around specific
 
 | Name | Description | Items | Tags |
 | ---- | ----------- | ----- | ---- |
-| [⭐ awesome-copilot](../plugins/awesome-copilot/README.md) | Meta prompts that help you discover and generate curated GitHub Copilot agents, collections, instructions, prompts, and skills. | 5 items | github-copilot, discovery, meta, prompt-engineering, agents |
+| [⭐ awesome-copilot](../plugins/awesome-copilot/README.md) | Meta prompts that help you discover and generate curated GitHub Copilot agents, instructions, prompts, and skills. | 5 items | github-copilot, discovery, meta, prompt-engineering, agents |
 | [⭐ copilot-sdk](../plugins/copilot-sdk/README.md) | Build applications with the GitHub Copilot SDK across multiple programming languages. Includes comprehensive instructions for C#, Go, Node.js/TypeScript, and Python to help you create AI-powered applications. | 5 items | copilot-sdk, sdk, csharp, go, nodejs, typescript, python, ai, github-copilot |
 | [⭐ partners](../plugins/partners/README.md) | Custom agents that have been created by GitHub partners | 20 items | devops, security, database, cloud, infrastructure, observability, feature-flags, cicd, migration, performance |
 | [azure-cloud-development](../plugins/azure-cloud-development/README.md) | Comprehensive Azure cloud development tools including Infrastructure as Code, serverless functions, architecture patterns, and cost optimization for building scalable cloud applications. | 18 items | azure, cloud, infrastructure, bicep, terraform, serverless, architecture, devops |
@@ -50,6 +50,7 @@ Curated plugins of related prompts, agents, and skills organized around specific
 | [project-planning](../plugins/project-planning/README.md) | Tools and guidance for software project planning, feature breakdown, epic management, implementation planning, and task organization for development teams. | 17 items | planning, project-management, epic, feature, implementation, task, architecture, technical-spike |
 | [python-mcp-development](../plugins/python-mcp-development/README.md) | Complete toolkit for building Model Context Protocol (MCP) servers in Python using the official SDK with FastMCP. Includes instructions for best practices, a prompt for generating servers, and an expert chat mode for guidance. | 3 items | python, mcp, model-context-protocol, fastmcp, server-development |
 | [ruby-mcp-development](../plugins/ruby-mcp-development/README.md) | Complete toolkit for building Model Context Protocol servers in Ruby using the official MCP Ruby SDK gem with Rails integration support. | 3 items | ruby, mcp, model-context-protocol, server-development, sdk, rails, gem |
+| [rug-agentic-workflow](../plugins/rug-agentic-workflow/README.md) | Three-agent workflow for orchestrated software delivery with an orchestrator plus implementation and QA subagents. | 3 items | agentic-workflow, orchestration, subagents, software-engineering, qa |
 | [rust-mcp-development](../plugins/rust-mcp-development/README.md) | Build high-performance Model Context Protocol servers in Rust using the official rmcp SDK with async/await, procedural macros, and type-safe implementations. | 3 items | rust, mcp, model-context-protocol, server-development, sdk, tokio, async, macros, rmcp |
 | [security-best-practices](../plugins/security-best-practices/README.md) | Security frameworks, accessibility guidelines, performance optimization, and code quality best practices for building secure, maintainable, and high-performance applications. | 6 items | security, accessibility, performance, code-quality, owasp, a11y, optimization, best-practices |
 | [software-engineering-team](../plugins/software-engineering-team/README.md) | 7 specialized agents covering the full software development lifecycle from UX design and architecture to security and DevOps. | 7 items | team, enterprise, security, devops, ux, architecture, product, ai-ethics |