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/openai_gateway_chat_completions.go

@@ -151,38 +151,23 @@ func (s *OpenAIGatewayService) ForwardAsChatCompletions(
 	}
 	logger.L().Debug("openai chat_completions: model mapping applied", logFields...)
 
-	{
+	if account.Type == AccountTypeOAuth {
 		var reqBody map[string]any
 		if err := json.Unmarshal(responsesBody, &reqBody); err != nil {
 			return nil, fmt.Errorf("unmarshal for codex transform: %w", err)
 		}
-		modified := false
-		if account.Type == AccountTypeOAuth {
-			codexResult := applyCodexOAuthTransform(reqBody, false, false)
-			modified = codexResult.Modified
-			if codexResult.NormalizedModel != "" {
-				upstreamModel = codexResult.NormalizedModel
-			}
-			if codexResult.PromptCacheKey != "" {
-				promptCacheKey = codexResult.PromptCacheKey
-			} else if promptCacheKey != "" {
-				reqBody["prompt_cache_key"] = promptCacheKey
-			}
-		} else {
-			// 非 OAuth 账号也需要提取 system 消息并注入 instructions，
-			// 否则上游 GPT-5/Codex 等模型会报 "Instructions are required"。
-			if extractSystemMessagesFromInput(reqBody) {
-				modified = true
-			}
-			if applyInstructions(reqBody, false) {
-				modified = true
-			}
+		codexResult := applyCodexOAuthTransform(reqBody, false, false)
+		if codexResult.NormalizedModel != "" {
+			upstreamModel = codexResult.NormalizedModel
 		}
-		if modified {
-			responsesBody, err = json.Marshal(reqBody)
-			if err != nil {
-				return nil, fmt.Errorf("remarshal after codex transform: %w", err)
-			}
+		if codexResult.PromptCacheKey != "" {
+			promptCacheKey = codexResult.PromptCacheKey
+		} else if promptCacheKey != "" {
+			reqBody["prompt_cache_key"] = promptCacheKey
+		}
+		responsesBody, err = json.Marshal(reqBody)
+		if err != nil {
+			return nil, fmt.Errorf("remarshal after codex transform: %w", err)
 		}
 	}