Notebooks: shared notebooks per QuestDB instance, stored server-side with permission-based access

Notebooks today are 100% client-side: persisted in the browser's IndexedDB (Dexie web-console DB — buffers.notebookViewState + the notebook_results table, src/store/db.ts, src/scenes/Editor/Notebook/useNotebookPersistence.ts). Nothing is stored server-side; the only sharing is file export/import (src/scenes/Editor/Monaco/exportTabs.ts / importTabs.ts). There is no notion of ownership, sharing, or read-only mode (only a per-query requireAllDQL check).

Request: "Shared notebooks" per instance — readable by all, or writable by multiple users — using QuestDB system tables + permissions. Real-time collaboration is explicitly out of scope.

Ask: persist shared notebooks in a server-side QuestDB table, gate read/write via QuestDB's permission/ACL system, and add UI to list/open shared vs. local notebooks. Reuse the existing NotebookViewState JSON serialization as the storage payload.

Start with src/store/db.ts and src/scenes/Editor/Notebook/useNotebookPersistence.ts to understand the existing NotebookViewState persistence, then review src/scenes/Editor/Monaco/exportTabs.ts and importTabs.ts for current sharing behavior. Check the existing requireAllDQL permission check and map the UI changes needed to list and open local versus shared notebooks. Done means shared notebooks are stored server-side, access follows permissions, and local notebooks continue to work without real-time collaboration.