revert: remove fork-only changes from release sync

Revert payment/wechat, sora/claude-max cleanup, fork-only migrations,
and cosmetic changes that were brought in by the release sync commit.
Keep only channel-monitor related improvements:
- PublicSettingsInjectionPayload named struct with drift test
- ChannelMonitorRunner graceful shutdown in wire
- image_output_price in SupportedModelChip
- Simplified buildSelfNavItems in AppSidebar
- Gateway WARN logs for 503 branches

backend/internal/service/gateway_hotpath_optimization_test.go

@@ -143,6 +143,7 @@ func (s *stickyGatewayCacheHotpathStub) RefreshSessionTTL(ctx context.Context, g
 func (s *stickyGatewayCacheHotpathStub) DeleteSessionAccountID(ctx context.Context, groupID int64, sessionHash string) error {
 	return nil
 }
+
 func (s *modelsListAccountRepoStub) ListSchedulableByGroupID(ctx context.Context, groupID int64) ([]Account, error) {
 	s.listByGroupCalls.Add(1)
 	if s.err != nil {