chore: remove all sora dead code and fork-specific sora_client_enabled

Upstream removed sora feature (090_drop_sora.sql) but left i18n keys
and wire.go references. Clean up:
- Remove entire sora i18n block from en.ts and zh.ts (~190 lines)
- Remove sora nav key and unused 'data' settings tab key
- Remove sora_client_enabled from settings (fork-specific)
- Remove SoraMediaCleanupService from wire.go

backend/cmd/server/wire.go

@@ -84,7 +84,6 @@ func provideCleanup(
 	opsCleanup *service.OpsCleanupService,
 	opsScheduledReport *service.OpsScheduledReportService,
 	opsSystemLogSink *service.OpsSystemLogSink,
-	soraMediaCleanup *service.SoraMediaCleanupService,
 	schedulerSnapshot *service.SchedulerSnapshotService,
 	tokenRefresh *service.TokenRefreshService,
 	accountExpiry *service.AccountExpiryService,
@@ -134,12 +133,6 @@ func provideCleanup(
 				}
 				return nil
 			}},
-			{"SoraMediaCleanupService", func() error {
-				if soraMediaCleanup != nil {
-					soraMediaCleanup.Stop()
-				}
-				return nil
-			}},
 			{"OpsAlertEvaluatorService", func() error {
 				if opsAlertEvaluator != nil {
 					opsAlertEvaluator.Stop()