Wrap the opts object and derived context in useMemo so ZeroReactProvider
receives stable references across parent re-renders. Before this change
opts was rebuilt on every render of ZeroProvider, which can cause the
Rocicorp Zero client to churn its internal state / reconnect if it
compares props by reference.
Fixes#1097.
- 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
