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/api/deps.py

@@ -1,12 +1,30 @@
-from fastapi import Depends, HTTPException, status
+import hmac
+
+from fastapi import Depends, Header, HTTPException, Request, status
 from fastapi.security import HTTPAuthorizationCredentials, HTTPBearer
 
+from app.core.config import settings
 from app.core.security import decode_token
 
-bearer = HTTPBearer()
+bearer = HTTPBearer(auto_error=False)
 
 
-def get_current_user(credentials: HTTPAuthorizationCredentials = Depends(bearer)) -> str:
+def get_current_user(
+    request: Request,
+    credentials: HTTPAuthorizationCredentials | None = Depends(bearer),
+    x_mcp_service_key: str | None = Header(default=None),
+) -> str:
+    # 1. MCP service key (Docker-internal only — backend port is not externally exposed)
+    if x_mcp_service_key is not None:
+        if not settings.mcp_service_key:
+            raise HTTPException(status_code=status.HTTP_401_UNAUTHORIZED, detail="MCP service key not configured")
+        if not hmac.compare_digest(x_mcp_service_key.encode(), settings.mcp_service_key.encode()):
+            raise HTTPException(status_code=status.HTTP_401_UNAUTHORIZED, detail="Invalid MCP service key")
+        return "__mcp_service__"
+
+    # 2. Standard JWT bearer token
+    if credentials is None:
+        raise HTTPException(status_code=status.HTTP_401_UNAUTHORIZED, detail="Not authenticated")
     username = decode_token(credentials.credentials)
     if not username:
         raise HTTPException(status_code=status.HTTP_401_UNAUTHORIZED, detail="Invalid token")

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"