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>

collections/csharp-dotnet-development.collection.yml

@@ -0,0 +1,22 @@
+id: csharp-dotnet-development
+name: C# .NET Development 
+description: Essential prompts, instructions, and chat modes for C# and .NET development including testing, documentation, and best practices.
+tags: [csharp, dotnet, aspnet, testing]
+items:
+  - path: prompts/csharp-async.prompt.md
+    kind: prompt
+  - path: prompts/aspnet-minimal-api-openapi.prompt.md
+    kind: prompt
+  - path: instructions/csharp.instructions.md
+    kind: instruction
+  - path: instructions/dotnet-architecture-good-practices.instructions.md
+    kind: instruction
+  - path: chatmodes/expert-dotnet-software-engineer.chatmode.md
+    kind: chat-mode
+  - path: prompts/csharp-xunit.prompt.md
+    kind: prompt
+  - path: prompts/dotnet-best-practices.prompt.md
+    kind: prompt
+display:
+  ordering: alpha
+  show_badge: false