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

frontend/src/utils/embedded-url.ts

@@ -1,6 +1,6 @@
 /**
  * Shared URL builder for iframe-embedded pages.
- * Used by PurchaseSubscriptionView and CustomPageView to build consistent URLs
+ * Used by CustomPageView to build consistent URLs
  * with user_id, token, theme, lang, ui_mode, src_host, and src parameters.
  */