feat: add MCP server with HTTP/SSE transport for AI integration

Exposes homelab topology to MCP-compatible AI clients (Claude Code, etc.)
over LAN via HTTP/SSE on port 8001.

- New mcp/ service: FastAPI + mcp SDK, SSE transport
- Auth: X-API-Key for AI clients, X-MCP-Service-Key for backend (Docker-internal)
- Resources: canvas, nodes, edges, scan/pending, scan/runs
- Tools: create/update/delete nodes+edges, trigger scan, approve/hide devices
- Backend deps.py: accepts JWT or MCP service key (no plain-text password)
- 40 tests (auth, resources, tools) across asyncio + trio
- docker-compose.yml: mcp service on port 8001
- README: MCP setup section with Claude Code/Desktop config examples

mcp/app/config.py

@@ -0,0 +1,12 @@
+from pydantic_settings import BaseSettings
+
+
+class Settings(BaseSettings):
+    mcp_api_key: str = "mcp_sk_changeme"       # AI client → MCP server
+    mcp_service_key: str = "svc_changeme"       # MCP server → backend
+    backend_url: str = "http://backend:8000"
+
+    model_config = {"env_file": ".env", "extra": "ignore"}
+
+
+settings = Settings()