## What kind of change does this PR introduce?
Feature, limited to staging and local.
## What is the current behavior?
On High Availability projects, Studio always disables Realtime: the
Realtime pages and the Publications pages show an "unavailable" message,
the table editor's "Enable Realtime" checkbox is disabled, and the
project home shows Realtime as disabled.
## What is the new behavior?
A new `useIsRealtimeUnavailable()` hook treats Realtime as unavailable
only on High Availability projects outside staging and local (via
`IS_STAGING_OR_LOCAL`). Those four places use it instead of checking
`high_availability` directly.
- **Production:** unchanged.
- **Staging and local:** Realtime behaves as on standard projects.
## Additional context
Whether a High Availability project is actually registered as a Realtime
tenant is gated separately on the platform side. Until then, the pages
render but Realtime connections for that project fail.
Tests: a new `resolveRealtimeUnavailable` test, and the
`TableRealtimeToggle` and `resolveRealtimeServiceStatus` tests updated
for the renamed parameter.
Ping-Min Lin
1ee88e0fee