Inbox filter reliability
- Moves large label/assignee conversation-list filtering into a service-role-only Postgres function so the app no longer has to encode hundreds of conversation IDs into a PostgREST GET URL.
- Keeps the existing keyset pagination and conversation hydration path while returning only a URL-safe page of filtered conversation IDs.
- Scopes
conversation_label_linksdirectly by workspace, removing an extra overflow-prone scoping query.