fix: align public_tools and public_notes sharing defaults with config (#27716)

The SharingPermissions model defaulted public_tools and public_notes to
True while the config defaults (USER_PERMISSIONS_WORKSPACE_TOOLS_ALLOW_PUBLIC_SHARING
and USER_PERMISSIONS_NOTES_ALLOW_PUBLIC_SHARING) are both False.

On an instance whose stored user.permissions config predates these keys,
GET /api/v1/users/default/permissions fills the gap from the model and
reports both as enabled, while has_permission fills it from
DEFAULT_USER_PERMISSIONS and denies. Saving any unrelated permission then
persists the model's True, granting public tool and note sharing the admin
never enabled.

backend/open_webui/routers/users.py

@@ -227,11 +227,11 @@ class SharingPermissions(BaseModel):
     prompts: bool = False
     public_prompts: bool = False
     tools: bool = False
-    public_tools: bool = True
+    public_tools: bool = False
     skills: bool = False
     public_skills: bool = False
     notes: bool = False
-    public_notes: bool = True
+    public_notes: bool = False
     folders: bool = False
     public_chats: bool = False
     public_calendars: bool = False