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/handler/admin/account_handler_mixed_channel_test.go

@@ -111,7 +111,7 @@ func TestAccountHandlerCreateMixedChannelConflictSimplifiedResponse(t *testing.T
 	var resp map[string]any
 	require.NoError(t, json.Unmarshal(rec.Body.Bytes(), &resp))
 	require.Equal(t, "mixed_channel_warning", resp["error"])
-	require.Contains(t, resp["message"], "claude-max")
+	require.Contains(t, resp["message"], "mixed_channel_warning")
 	_, hasDetails := resp["details"]
 	_, hasRequireConfirmation := resp["require_confirmation"]
 	require.False(t, hasDetails)
@@ -140,7 +140,7 @@ func TestAccountHandlerUpdateMixedChannelConflictSimplifiedResponse(t *testing.T
 	var resp map[string]any
 	require.NoError(t, json.Unmarshal(rec.Body.Bytes(), &resp))
 	require.Equal(t, "mixed_channel_warning", resp["error"])
-	require.Contains(t, resp["message"], "claude-max")
+	require.Contains(t, resp["message"], "mixed_channel_warning")
 	_, hasDetails := resp["details"]
 	_, hasRequireConfirmation := resp["require_confirmation"]
 	require.False(t, hasDetails)

backend/internal/handler/admin/setting_handler.go

@@ -235,9 +235,11 @@ func (h *SettingHandler) GetSettings(c *gin.Context) {
 		PaymentCancelRateLimitWindow:           paymentCfg.CancelRateLimitWindow,
 		PaymentCancelRateLimitUnit:             paymentCfg.CancelRateLimitUnit,
 		PaymentCancelRateLimitMode:             paymentCfg.CancelRateLimitMode,
-		ChannelMonitorEnabled:                  settings.ChannelMonitorEnabled,
-		ChannelMonitorDefaultIntervalSeconds:   settings.ChannelMonitorDefaultIntervalSeconds,
-		AvailableChannelsEnabled:               settings.AvailableChannelsEnabled,
+
+		ChannelMonitorEnabled:                settings.ChannelMonitorEnabled,
+		ChannelMonitorDefaultIntervalSeconds: settings.ChannelMonitorDefaultIntervalSeconds,
+
+		AvailableChannelsEnabled: settings.AvailableChannelsEnabled,
 	}
 	response.Success(c, systemSettingsResponseData(payload, authSourceDefaults))
 }
@@ -1477,9 +1479,11 @@ func (h *SettingHandler) UpdateSettings(c *gin.Context) {
 		PaymentCancelRateLimitWindow:           updatedPaymentCfg.CancelRateLimitWindow,
 		PaymentCancelRateLimitUnit:             updatedPaymentCfg.CancelRateLimitUnit,
 		PaymentCancelRateLimitMode:             updatedPaymentCfg.CancelRateLimitMode,
-		ChannelMonitorEnabled:                  updatedSettings.ChannelMonitorEnabled,
-		ChannelMonitorDefaultIntervalSeconds:   updatedSettings.ChannelMonitorDefaultIntervalSeconds,
-		AvailableChannelsEnabled:               updatedSettings.AvailableChannelsEnabled,
+
+		ChannelMonitorEnabled:                updatedSettings.ChannelMonitorEnabled,
+		ChannelMonitorDefaultIntervalSeconds: updatedSettings.ChannelMonitorDefaultIntervalSeconds,
+
+		AvailableChannelsEnabled: updatedSettings.AvailableChannelsEnabled,
 	}
 	response.Success(c, systemSettingsResponseData(payload, updatedAuthSourceDefaults))
 }

backend/internal/handler/dto/public_settings_injection_schema_test.go

@@ -31,6 +31,8 @@ func TestPublicSettingsInjectionPayload_SchemaDoesNotDrift(t *testing.T) {
 	dtoOnlyFields := map[string]string{
 		// sora_client_enabled is an upstream-only field the fork does not surface.
 		"sora_client_enabled": "upstream-only field, not used on this fork",
+		// force_email_on_third_party_signup lives on the DTO but is not injected via SSR.
+		"force_email_on_third_party_signup": "auth-source default, not a feature flag",
 	}
 
 	var missing []string