fix: strip model params for read-only callers in the model list endpoint (#27004)

The per-id model endpoint (GET /api/v1/models/model) strips params, the system
prompt and other curated model config, for callers who only have read access.
The list endpoint (GET /api/v1/models/list) did not: it returned each
read-accessible model's full params, so a read-shared model exposed its
params.system to non-owner read-grant holders.

Mirror the per-id behaviour: compute write_access per item and drop params
before serialising when the caller lacks write access (not the owner, not an
admin under BYPASS_ADMIN_ACCESS_CONTROL and holding no write grant). The
model-card list UI does not render params, so this does not change
functionality.

Co-authored-by: bogdancherniy11-sudo <229690748+bogdancherniy11-sudo@users.noreply.github.com>

backend/open_webui/routers/models.py

@@ -189,16 +189,16 @@ async def get_models(
         data = add_chat_variables_schema(model.model_dump())
         if data.get('meta'):
             data['meta'].pop('profile_image_url', None)
-        items.append(
-            ModelAccessResponse(
-                **data,
-                write_access=(
-                    (user.role == 'admin' and BYPASS_ADMIN_ACCESS_CONTROL)
-                    or user.id == model.user_id
-                    or model.id in writable_model_ids
-                ),
-            )
+        write_access = (
+            (user.role == 'admin' and BYPASS_ADMIN_ACCESS_CONTROL)
+            or user.id == model.user_id
+            or model.id in writable_model_ids
         )
+        # Strip params (system prompt and other curated config) for read-only
+        # callers, mirroring the per-id endpoint.
+        if not write_access:
+            data['params'] = {}
+        items.append(ModelAccessResponse(**data, write_access=write_access))
 
     return ModelAccessListResponse(
         items=items,