fix(security): enforce registered endpoint authority

Require caller-supplied model endpoints to resolve through enabled owner-visible registrations, harden session path encoding, and remove the SVG title HTML parsing sink.

routes/assistant_routes.py

@@ -16,6 +16,7 @@ from pydantic import BaseModel
 
 from core.database import SessionLocal, CrewMember, ScheduledTask
 from src.auth_helpers import get_current_user
+from src.endpoint_resolver import resolve_owner_registered_endpoint_url
 from src.owner_identity import REQUEST_SENTINEL_OWNERS
 from src.task_scheduler import compute_next_run
 
@@ -178,7 +179,13 @@ def setup_assistant_routes(task_scheduler) -> APIRouter:
             if payload.model is not None:
                 crew_db.model = payload.model or None
             if payload.endpoint_url is not None:
-                crew_db.endpoint_url = payload.endpoint_url or None
+                try:
+                    crew_db.endpoint_url = (
+                        resolve_owner_registered_endpoint_url(db, payload.endpoint_url, owner)
+                        if payload.endpoint_url else None
+                    )
+                except ValueError as exc:
+                    raise HTTPException(400, str(exc)) from exc
             if payload.timezone is not None:
                 crew_db.timezone = payload.timezone or None