fix(router): restore BYOK key injection for vector store endpoints with team-scoped deployments

When vector store endpoints (POST/GET /v1/vector_stores) are called, model=None
is passed to the router. map_team_model(None, team_id) was returning None
unchanged after the team model routing fix in #25148, so the router never found
the team's BYOK deployment and forwarded requests without the API key.

Fix: when team_model_name is None, return the matched deployment's
team_public_model_name (or model_name fallback) so the router can route to it
and inject the BYOK credentials. Does not affect the sibling-deployment
load-balancing fix since that only applies when a non-None model is passed.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

litellm/router.py

@@ -8281,7 +8281,9 @@ class Router:
         # No match found
         return None
 
-    def map_team_model(self, team_model_name: str, team_id: str) -> Optional[str]:
+    def map_team_model(
+        self, team_model_name: Optional[str], team_id: str
+    ) -> Optional[str]:
         """
         Check if team_model_name resolves to team-specific deployments.
 
@@ -8289,6 +8291,11 @@ class Router:
         sibling deployments via team_id filtering, instead of collapsing to a
         single internal model_name.
 
+        When team_model_name is None (e.g. vector store / file endpoints that
+        don't include a model in their request), returns the first matching
+        team deployment's team_public_model_name so the router can inject BYOK
+        credentials from the team-scoped deployment.
+
         Returns:
         - str: the team_model_name if team deployments exist for this team
         - None: if no team-specific model is found
@@ -8298,6 +8305,13 @@ class Router:
             return None
         for model in models:
             if model.get("model_info", {}).get("team_id") == team_id:
+                if team_model_name is None:
+                    # No model was specified (e.g. vector store endpoints).
+                    # Return the deployment's public model name so the router
+                    # can route to it and inject the BYOK API key.
+                    return model.get("model_info", {}).get(
+                        "team_public_model_name"
+                    ) or model.get("model_name")
                 return team_model_name
 
         # No team-scoped deployment found; wildcard/pattern routes are