feat: add .NET backend development plugin (#157)

Co-authored-by: Martineto21 <ramac21@gmail.com>

plugins/dotnet-contribution/README.md

@@ -0,0 +1,127 @@
+# .NET Backend Development Plugin
+
+A comprehensive plugin for .NET backend development with C#, ASP.NET Core, Entity Framework Core, and Dapper.
+
+## Overview
+
+This plugin provides agents, skills, and patterns for building production-grade .NET applications. It focuses on modern C# (12/13), ASP.NET Core 8+, and enterprise development patterns.
+
+## Contents
+
+### Agents
+
+| Agent | Model | Description |
+|-------|-------|-------------|
+| `dotnet-architect` | Sonnet | Expert .NET architect for API development, code review, and architecture decisions |
+
+### Skills
+
+| Skill | Description |
+|-------|-------------|
+| `dotnet-backend-patterns` | Comprehensive patterns for services, repositories, DI, caching, and testing |
+
+### Assets
+
+- `service-template.cs` - Complete service implementation with Result pattern, validation, caching
+- `repository-template.cs` - Repository implementations with Dapper and EF Core
+
+### References
+
+- `ef-core-best-practices.md` - EF Core optimization guide
+- `dapper-patterns.md` - Advanced Dapper usage patterns
+
+## Usage
+
+### With Claude Code CLI
+
+```bash
+# General .NET architecture help
+claude -p "Act as dotnet-architect and design a caching strategy for my product catalog"
+
+# Code review
+claude -p "Act as dotnet-architect and review this async code for issues"
+
+# Implementation help
+claude -p "Use dotnet-backend-patterns skill to implement a repository with Dapper"
+```
+
+### Example Prompts
+
+1. **API Design**
+   ```
+   Act as dotnet-architect. Design a REST API for order management with proper 
+   DTOs, validation, and error handling.
+   ```
+
+2. **Performance Review**
+   ```
+   Act as dotnet-architect. Review this EF Core query for N+1 problems and 
+   suggest optimizations.
+   ```
+
+3. **Architecture Decision**
+   ```
+   Act as dotnet-architect. Should I use EF Core or Dapper for this high-throughput 
+   read scenario? Explain trade-offs.
+   ```
+
+## Topics Covered
+
+### C# Language
+- Async/await patterns and pitfalls
+- LINQ optimization
+- Records and immutability
+- Pattern matching
+- Nullable reference types
+- Memory-efficient programming
+
+### ASP.NET Core
+- Minimal APIs and Controllers
+- Dependency Injection (Scoped, Singleton, Transient, Keyed)
+- Configuration with IOptions
+- Middleware pipeline
+- Authentication/Authorization
+- Health checks
+
+### Data Access
+- Entity Framework Core best practices
+- Dapper for high-performance queries
+- Repository pattern
+- Unit of Work
+- Connection management
+- Transaction handling
+
+### Caching
+- IMemoryCache
+- IDistributedCache with Redis
+- Multi-level caching
+- Cache invalidation
+- Distributed locking
+
+### Testing
+- xUnit fundamentals
+- Moq for mocking
+- Integration tests with WebApplicationFactory
+- Test patterns and best practices
+
+## Stack Compatibility
+
+| Technology | Version |
+|------------|---------|
+| .NET | 8.0+ |
+| C# | 12+ |
+| ASP.NET Core | 8.0+ |
+| Entity Framework Core | 8.0+ |
+| SQL Server | 2019+ |
+| Redis | 6.0+ |
+
+## Contributing
+
+Contributions welcome! Please ensure:
+- Code examples compile and follow C# conventions
+- Patterns are production-tested
+- Documentation is clear and includes examples
+
+## License
+
+MIT License - See repository root for details.