Fix review feedback: mode→agent frontmatter, add applyTo, generate plugin

- Fix prompt frontmatter: mode: 'agent' → agent: 'agent' (repo convention)
- Add applyTo: '**' to instructions file
- Remove trailing Claude credit from instructions
- Generate plugin via npm run plugin:migrate
- Rebase onto latest upstream/main

plugins/context-engineering/README.md

@@ -0,0 +1,34 @@
+# Context Engineering Plugin
+
+Tools and techniques for maximizing GitHub Copilot effectiveness through better context management. Includes guidelines for structuring code, an agent for planning multi-file changes, and prompts for context-aware development.
+
+## Installation
+
+```bash
+# Using Copilot CLI
+copilot plugin install context-engineering@awesome-copilot
+```
+
+## What's Included
+
+### Commands (Slash Commands)
+
+| Command | Description |
+|---------|-------------|
+| `/context-engineering:context-map` | Generate a map of all files relevant to a task before making changes |
+| `/context-engineering:what-context-needed` | Ask Copilot what files it needs to see before answering a question |
+| `/context-engineering:refactor-plan` | Plan a multi-file refactor with proper sequencing and rollback steps |
+
+### Agents
+
+| Agent | Description |
+|-------|-------------|
+| `context-architect` | An agent that helps plan and execute multi-file changes by identifying relevant context and dependencies |
+
+## Source
+
+This plugin is part of [Awesome Copilot](https://github.com/github/awesome-copilot), a community-driven collection of GitHub Copilot extensions.
+
+## License
+
+MIT