Calendar Connection Health

Live-verify the org's active calendar connection.

GET /connections only reports the stored is_active flag — which stays true even after the OAuth token silently expires or is revoked, so the new-interview page cheerfully shows "Calendar connected" while Meet auto-create is actually dead (the exact misleading-indicator bug this fixes). This endpoint instead calls get_credentials(), which attempts a real token refresh and marks the connection inactive on RefreshError. So: • healthy=true → token is live, auto-create will work • needs_reconnect=true → connection exists but its token is dead; the FE shows "Calendar needs reconnecting" • connected=false → no active connection at all

Kept cheap (credential refresh only, no events list) so it's fine to call once on page load. The refresh persists a fresh access token as a side effect, so this doubles as passive token upkeep.