Implement Collections feature for grouping related prompts, instructions, and chat modes (#232)

* Initial plan

* Implement core Collections feature with YAML parsing and README generation

Co-authored-by: aaronpowell <434140+aaronpowell@users.noreply.github.com>

* Complete Collections feature implementation with validation, tooling, and documentation

Co-authored-by: aaronpowell <434140+aaronpowell@users.noreply.github.com>

* Update generated README files to include collections instructions

* Fix YAML parsing logic bug: replace impossible condition with proper indentation check

Co-authored-by: aaronpowell <434140+aaronpowell@users.noreply.github.com>

* Refactor: Extract YAML parser to shared module and improve user experience

Co-authored-by: aaronpowell <434140+aaronpowell@users.noreply.github.com>

* fixing task and file permissions

* Better args handling

* Adding some more collections

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: aaronpowell <434140+aaronpowell@users.noreply.github.com>
Co-authored-by: Aaron Powell <me@aaron-powell.com>

instructions/collections.instructions.md

@@ -0,0 +1,54 @@
+---
+description: 'Guidelines for creating and managing awesome-copilot collections'
+applyTo: 'collections/*.collection.yml'
+---
+
+# Collections Development
+
+## Collection Instructions
+
+When working with collections in the awesome-copilot repository:
+
+- Always validate collections using `node validate-collections.js` before committing
+- Follow the established YAML schema for collection manifests
+- Reference only existing files in the repository
+- Use descriptive collection IDs with lowercase letters, numbers, and hyphens
+- Keep collections focused on specific workflows or themes
+- Test that all referenced items work well together
+
+## Collection Structure
+
+- **Required fields**: id, name, description, items
+- **Optional fields**: tags, display
+- **Item requirements**: path must exist, kind must match file extension
+- **Display options**: ordering (alpha/manual), show_badge (true/false)
+
+## Validation Rules
+
+- Collection IDs must be unique across all collections
+- File paths must exist and match the item kind
+- Tags must use lowercase letters, numbers, and hyphens only
+- Collections must contain 1-50 items
+- Descriptions must be 1-500 characters
+
+## Best Practices
+
+- Group 3-10 related items for optimal usability  
+- Use clear, descriptive names and descriptions
+- Add relevant tags for discoverability
+- Test the complete workflow the collection enables
+- Ensure items complement each other effectively
+
+## File Organization
+
+- Collections don't require file reorganization
+- Items can be located anywhere in the repository
+- Use relative paths from repository root
+- Maintain existing directory structure (prompts/, instructions/, chatmodes/)
+
+## Generation Process
+
+- Collections automatically generate README files via `update-readme.js`
+- Individual collection pages are created in collections/ directory
+- Main collections overview is generated as README.collections.md
+- VS Code install badges are automatically created for each item