feat(openai): 完善 Chat 与 Responses 参数转发

原生 Chat/Responses 改为透明转发，保留标准工具结构并保护调用方显式参数。补齐 Responses 到 Chat 的兼容转换、协议路由边界、完整响应和流式事件，并同步更新 Swagger、回归测试与真实验收脚本。

验证：
- cd apps/api && env -u AI_GATEWAY_TEST_DATABASE_URL go test ./... -count=1
- pnpm openapi
- pnpm lint
- pnpm test
- pnpm build
- gofmt -l 无输出
- git diff --check 通过

风险：
- Chat 回退无法等价表达的 Responses 原生能力现在会返回 unsupported_response_parameter
- 真实供应商 E2E 因本地没有已启用的平台模型候选而未完成

apps/api/internal/httpapi/streaming.go

@@ -49,7 +49,7 @@ func (s *compatibleStreamWriter) writeDelta(w http.ResponseWriter, event clients
 				if sequence := intFromStreamValue(event.Event["sequence_number"]); sequence >= s.responseSequence {
 					s.responseSequence = sequence + 1
 				}
-				if eventType == "response.completed" {
+				if isResponsesTerminalEvent(eventType) {
 					s.sentResponseDone = true
 				}
 				sendSSE(w, eventType, event.Event)
@@ -84,7 +84,8 @@ func (s *compatibleStreamWriter) writeDone(w http.ResponseWriter, output map[str
 		if s.sentResponseDone {
 			return
 		}
-		sendSSE(w, "response.completed", map[string]any{"type": "response.completed", "sequence_number": s.responseSequence, "response": output})
+		eventType := responsesTerminalEvent(output)
+		sendSSE(w, eventType, map[string]any{"type": eventType, "sequence_number": s.responseSequence, "response": output})
 		s.sentResponseDone = true
 		return
 	}
@@ -106,6 +107,28 @@ func (s *compatibleStreamWriter) writeDone(w http.ResponseWriter, output map[str
 	s.writeDoneMarker(w)
 }
 
+func isResponsesTerminalEvent(eventType string) bool {
+	switch eventType {
+	case "response.completed", "response.incomplete", "response.failed", "response.cancelled":
+		return true
+	default:
+		return false
+	}
+}
+
+func responsesTerminalEvent(output map[string]any) string {
+	switch status, _ := output["status"].(string); status {
+	case "incomplete":
+		return "response.incomplete"
+	case "failed":
+		return "response.failed"
+	case "cancelled":
+		return "response.cancelled"
+	default:
+		return "response.completed"
+	}
+}
+
 func intFromStreamValue(value any) int {
 	switch typed := value.(type) {
 	case int: