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/pricing_service_test.go

@@ -128,6 +128,21 @@ func TestGetModelPricing_Gpt54NanoUsesDedicatedStaticFallbackWhenRemoteMissing(t
 	require.Zero(t, got.LongContextInputTokenThreshold)
 }
 
+func TestGetModelPricing_ImageModelDoesNotFallbackToTextModel(t *testing.T) {
+	imagePricing := &LiteLLMModelPricing{InputCostPerToken: 3}
+	textPricing := &LiteLLMModelPricing{InputCostPerToken: 9}
+
+	svc := &PricingService{
+		pricingData: map[string]*LiteLLMModelPricing{
+			"gpt-image-2": imagePricing,
+			"gpt-5.4":     textPricing,
+		},
+	}
+
+	got := svc.GetModelPricing("gpt-image-3")
+	require.Same(t, imagePricing, got)
+}
+
 func TestParsePricingData_PreservesPriorityAndServiceTierFields(t *testing.T) {
 	raw := map[string]any{
 		"gpt-5.4": map[string]any{