feat(#132): port MCP (Model Context Protocol) infrastructure

Implement MCP Phase 1 infrastructure for agent tool integration with
central hub, tool registry, and STDIO transport layers.

Components:
- McpHubService: Central registry for MCP server lifecycle
- StdioTransport: STDIO process communication with JSON-RPC 2.0
- ToolRegistryService: Tool catalog management
- McpController: REST API for MCP management

Endpoints:
- GET/POST /mcp/servers - List/register servers
- POST /mcp/servers/:id/start|stop - Lifecycle control
- DELETE /mcp/servers/:id - Unregister
- GET /mcp/tools - List tools
- POST /mcp/tools/:name/invoke - Invoke tool

Features:
- Full JSON-RPC 2.0 protocol support
- Process lifecycle management
- Buffered message parsing
- Type-safe with no explicit any types
- Proper cleanup on shutdown

Tests: 85 passing with 90.9% coverage

Fixes #132

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

apps/api/src/mcp/dto/index.ts

@@ -0,0 +1 @@
+export * from "./register-server.dto";

apps/api/src/mcp/dto/register-server.dto.ts

@@ -0,0 +1,26 @@
+import { IsString, IsOptional, IsObject } from "class-validator";
+
+/**
+ * DTO for registering a new MCP server
+ */
+export class RegisterServerDto {
+  @IsString()
+  id!: string;
+
+  @IsString()
+  name!: string;
+
+  @IsString()
+  description!: string;
+
+  @IsString()
+  command!: string;
+
+  @IsOptional()
+  @IsString({ each: true })
+  args?: string[];
+
+  @IsOptional()
+  @IsObject()
+  env?: Record<string, string>;
+}