Add OpenAPI-to-Application collections for 5 common frameworks

Add 5 framework-specific collections with shared agent and prompt for generating production-ready applications from OpenAPI specifications:
- Java Spring Boot
- Python FastAPI
- Node.js NestJS
- C# .NET
- Go

Reuses existing framework instructions for consistency and best practices.

collections/openapi-to-application-csharp-dotnet.collection.yml

@@ -0,0 +1,14 @@
+id: openapi-to-application-csharp-dotnet
+name: OpenAPI to Application - C# .NET
+description: 'Generate production-ready .NET applications from OpenAPI specifications. Includes ASP.NET Core project scaffolding, controller generation, entity framework integration, and C# best practices.'
+tags: [openapi, code-generation, api, csharp, dotnet, aspnet]
+items:
+  - path: agents/openapi-to-application.agent.md
+    kind: agent
+  - path: instructions/csharp.instructions.md
+    kind: instruction
+  - path: prompts/openapi-to-application-code.prompt.md
+    kind: prompt
+display:
+  ordering: manual
+  show_badge: false