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- Remove collections.instructions.md (no longer applicable)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

eng/constants.mjs

@@ -36,27 +36,6 @@ Ready-to-use prompt templates for specific development scenarios and tasks, defi
 - Run the \`Chat: Run Prompt\` command from the Command Palette
 - Hit the run button while you have a prompt file open in VS Code`,
 
-  collectionsSection: `## 📦 Collections
-
-Curated collections of related prompts, instructions, and agents organized around specific themes, workflows, or use cases.`,
-
-  collectionsUsage: `### How to Use Collections
-
-**Browse Collections:**
-- ⭐ Featured collections are highlighted and appear at the top of the list
-- Explore themed collections that group related customizations
-- Each collection includes prompts, instructions, and agents for specific workflows
-- Collections make it easy to adopt comprehensive toolkits for particular scenarios
-
-**Install Items:**
-- Click install buttons for individual items within collections
-- Or browse to the individual files to copy content manually
-- Collections help you discover related customizations you might have missed`,
-
-  featuredCollectionsSection: `## 🌟 Featured Collections
-
-Discover our curated collections of prompts, instructions, and agents organized around specific themes and workflows.`,
-
   pluginsSection: `## 🔌 Plugins
 
 Curated plugins of related prompts, agents, and skills organized around specific themes, workflows, or use cases. Plugins can be installed directly via GitHub Copilot CLI.`,

eng/contributor-report.mjs

@@ -19,8 +19,6 @@ setupGracefulShutdown('contributor-report');
 export const AUTO_GENERATED_PATTERNS = [
   'README.md',
   'README.*.md',
-  'collections/*.md',
-  'collections/*.collection.md',
   'docs/README.*.md',
   'docs/*.generated.md'
 ];
@@ -42,8 +40,8 @@ export const TYPE_PATTERNS = {
   skills: [
     'skills/'
   ],
-  collections: [
-    'collections/*.collection.yml'
+  plugins: [
+    'plugins/**/plugin.json'
   ],
   doc: [
     'docs/**/*.md',