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>

docs/stories/sprint_5/story_5_6.md

@@ -0,0 +1,128 @@
+---
+story_id: story_5_6
+sprint_id: sprint_5
+phase: Phase 2 - Resources
+status: not_started
+priority: P0
+story_points: 3
+assignee: backend
+estimated_days: 1
+created_date: 2025-11-06
+dependencies: [story_5_5]
+---
+
+# Story 5.6: Resource Registration & Discovery
+
+**Phase**: Phase 2 - Resources (Week 3-4)
+**Priority**: P0 CRITICAL
+**Estimated Effort**: 3 Story Points (1 day)
+
+## User Story
+
+**As an** AI Agent
+**I want** to discover available MCP Resources dynamically
+**So that** I know what data I can access from ColaFlow
+
+## Business Value
+
+Dynamic Resource discovery enables:
+- AI agents to explore available capabilities
+- Easy addition of new Resources without code changes
+- Version compatibility checking
+- Documentation generation
+
+## Acceptance Criteria
+
+### AC1: Auto-Discovery
+- [ ] All `IMcpResource` implementations auto-registered at startup
+- [ ] Use Assembly scanning (Reflection)
+- [ ] Singleton registration in DI container
+
+### AC2: Resource Catalog
+- [ ] `resources/list` method returns all Resources
+- [ ] Each Resource includes: URI, name, description, MIME type
+- [ ] Response conforms to MCP specification
+
+### AC3: Resource Versioning
+- [ ] Support for Resource versioning (future-proof)
+- [ ] Optional `version` field in Resource metadata
+
+### AC4: Configuration
+- [ ] Enable/disable Resources via `appsettings.json`
+- [ ] Filter Resources by tenant (optional)
+
+### AC5: Testing
+- [ ] Unit tests for registry logic
+- [ ] Integration test for `resources/list`
+
+## Technical Design
+
+```csharp
+public interface IMcpRegistry
+{
+    void RegisterResource(IMcpResource resource);
+    IMcpResource? GetResource(string uri);
+    IReadOnlyList<IMcpResource> GetAllResources();
+}
+
+public class McpRegistry : IMcpRegistry
+{
+    private readonly Dictionary<string, IMcpResource> _resources = new();
+
+    public void RegisterResource(IMcpResource resource)
+    {
+        _resources[resource.Uri] = resource;
+    }
+
+    public IMcpResource? GetResource(string uri)
+    {
+        return _resources.TryGetValue(uri, out var resource) ? resource : null;
+    }
+
+    public IReadOnlyList<IMcpResource> GetAllResources()
+    {
+        return _resources.Values.ToList().AsReadOnly();
+    }
+}
+
+// Auto-registration
+public static class McpServiceExtensions
+{
+    public static IServiceCollection AddMcpResources(
+        this IServiceCollection services)
+    {
+        var assembly = typeof(IMcpResource).Assembly;
+        var resourceTypes = assembly.GetTypes()
+            .Where(t => typeof(IMcpResource).IsAssignableFrom(t)
+                && !t.IsInterface && !t.IsAbstract);
+
+        foreach (var type in resourceTypes)
+        {
+            services.AddSingleton(typeof(IMcpResource), type);
+        }
+
+        services.AddSingleton<IMcpRegistry, McpRegistry>();
+        return services;
+    }
+}
+```
+
+## Tasks
+
+- [ ] Create `IMcpRegistry` interface (1 hour)
+- [ ] Implement `McpRegistry` class (2 hours)
+- [ ] Implement auto-discovery via Reflection (2 hours)
+- [ ] Implement `resources/list` handler (1 hour)
+- [ ] Add configuration support (1 hour)
+- [ ] Unit tests (2 hours)
+
+## Definition of Done
+
+- [ ] All Resources auto-registered
+- [ ] `resources/list` returns complete catalog
+- [ ] Unit tests passing
+- [ ] Code reviewed
+
+## Reference
+
+- MCP Spec: https://modelcontextprotocol.io/docs/concepts/resources