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/pricing_service.go

@@ -812,16 +812,6 @@ func (s *PricingService) matchOpenAIModel(model string) *LiteLLMModelPricing {
 		return openAIGPT54FallbackPricing
 	}
 
-	if isOpenAIImageGenerationModel(model) {
-		for _, candidate := range []string{"gpt-image-2", "gpt-image-1.5", "gpt-image-1"} {
-			if pricing, ok := s.pricingData[candidate]; ok {
-				logger.LegacyPrintf("service.pricing", "[Pricing] OpenAI image fallback matched %s -> %s", model, candidate)
-				return pricing
-			}
-		}
-		return nil
-	}
-
 	// 最终回退到 DefaultTestModel
 	defaultModel := strings.ToLower(openai.DefaultTestModel)
 	if pricing, ok := s.pricingData[defaultModel]; ok {