sync: bring over remaining release/custom-0.1.115 changes

- Extract PublicSettingsInjectionPayload named struct with drift test
- Add channel_monitor_default_interval_seconds to SSR injection
- Add image_output_price to SupportedModelChip
- Simplify AppSidebar buildSelfNavItems (admins see available channels)
- Add gateway WARN logs for 503 no-available-accounts branches
- Wire ChannelMonitorRunner into provideCleanup for graceful shutdown
- Add migrations 130/131 (CC template userid fix + mimicry field cleanup)
- Clean up fork-only features (sora, claude max simulation, client affinity)
- Remove ~320 obsolete i18n keys
- Add codexUsage utility, WechatServiceButton, BulkEditAccountModal
- Tidy go.sum

backend/internal/service/concurrency_service_test.go

@@ -87,6 +87,7 @@ func (c *stubConcurrencyCacheForTest) GetAccountsLoadBatch(_ context.Context, _
 func (c *stubConcurrencyCacheForTest) GetUsersLoadBatch(_ context.Context, _ []UserWithConcurrency) (map[int64]*UserLoadInfo, error) {
 	return c.usersLoadBatch, c.usersLoadErr
 }
+
 func (c *stubConcurrencyCacheForTest) CleanupExpiredAccountSlots(_ context.Context, _ int64) error {
 	return c.cleanupErr
 }