feat(backend): Implement MCP Protocol Handler (Story 5.1)
Implemented JSON-RPC 2.0 protocol handler for MCP communication, enabling AI agents to communicate with ColaFlow using the Model Context Protocol.
**Implementation:**
- JSON-RPC 2.0 data models (Request, Response, Error, ErrorCode)
- MCP protocol models (Initialize, Capabilities, ClientInfo, ServerInfo)
- McpProtocolHandler with method routing and error handling
- Method handlers: initialize, resources/list, tools/list, tools/call
- ASP.NET Core middleware for /mcp endpoint
- Service registration and dependency injection setup
**Testing:**
- 28 unit tests covering protocol parsing, validation, and error handling
- Integration tests for initialize handshake and error responses
- All tests passing with >80% coverage
**Changes:**
- Created ColaFlow.Modules.Mcp.Contracts project
- Created ColaFlow.Modules.Mcp.Domain project
- Created ColaFlow.Modules.Mcp.Application project
- Created ColaFlow.Modules.Mcp.Infrastructure project
- Created ColaFlow.Modules.Mcp.Tests project
- Registered MCP module in ColaFlow.API Program.cs
- Added /mcp endpoint via middleware
**Acceptance Criteria Met:**
✅ JSON-RPC 2.0 messages correctly parsed
✅ Request validation (jsonrpc: "2.0", method, params, id)
✅ Error responses conform to JSON-RPC 2.0 spec
✅ Invalid requests return proper error codes (-32700, -32600, -32601, -32602)
✅ MCP initialize method implemented
✅ Server capabilities returned (resources, tools, prompts)
✅ Protocol version negotiation works (1.0)
✅ Request routing to method handlers
✅ Unit test coverage > 80%
✅ All tests passing
**Story**: docs/stories/sprint_5/story_5_1.md
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
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