fix(monitor): harden server delete and remove challenge docs

- Delete server state before monitored server to avoid FK 500s
- Keep legacy cleanup for obsolete challenge tables
- Rewrite monitor docs to API key-only flow

app/api/routers/monitor.py

@@ -5,6 +5,7 @@ from typing import List
 
 from fastapi import APIRouter, Depends, Header, HTTPException, status
 from pydantic import BaseModel
+from sqlalchemy import text
 from sqlalchemy.orm import Session
 
 from app.core.config import get_db
@@ -132,9 +133,20 @@ def delete_server(server_id: int, db: Session = Depends(get_db), _: models.User
     obj = db.query(MonitoredServer).filter(MonitoredServer.id == server_id).first()
     if not obj:
         raise HTTPException(status_code=404, detail='Server not found')
-    state = db.query(ServerState).filter(ServerState.server_id == server_id).first()
-    if state:
-        db.delete(state)
+
+    # Delete dependent rows first to avoid FK errors.
+    db.query(ServerState).filter(ServerState.server_id == server_id).delete(synchronize_session=False)
+
+    # Backward-compatible cleanup for deprecated challenge tables that may still exist in older DBs.
+    try:
+        db.execute(text('DELETE FROM server_handshake_nonces WHERE server_id = :server_id'), {'server_id': server_id})
+    except Exception:
+        pass
+    try:
+        db.execute(text('DELETE FROM server_challenges WHERE server_id = :server_id'), {'server_id': server_id})
+    except Exception:
+        pass
+
     db.delete(obj)
     db.commit()
     return None