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

backend/app/core/config.py

@@ -25,6 +25,11 @@ class Settings(BaseSettings):
     # Status checker
     status_checker_interval: int = 60
 
+    # MCP service key — set MCP_SERVICE_KEY in .env
+    # Used by the MCP server to authenticate against the backend without a user password.
+    # Leave empty to disable MCP service key auth.
+    mcp_service_key: str = ""
+
     def _override_path(self) -> Path:
         return Path(self.sqlite_path).parent / "scan_config.json"