- Fix timestamp conversion: String(epochMs) → new Date(epochMs).toISOString()
in use-messages-sync, use-comments-sync, use-documents, use-inbox.
Without this, date comparisons (isEdited, cutoff filters) would fail.
- Fix updated_at: undefined → null in use-inbox to match InboxItem type
- Fix ZeroProvider: skip Zero connection for unauthenticated users
- Clean 30+ stale "Electric SQL" comments in backend Python code