feat: P1 长文本分段合成

- 新增 text_splitter.py: 长文本智能分段（句子边界 + 短段合并）
- 新增 audio_merger.py: FFmpeg concat 音频合并器
- workflow.py: 分段合成完整流程（同步合并 / 异步轮询 / 失败处理）
- tts_synthesis.py: 新增 process_tts_segment_synthesis Celery 任务
- tts.py: 路由层自动识别分段任务并分发到对应 Celery task
- 23 个单元测试全部通过，P0 回归测试无退化

apps/api/app/api/routes/tts.py

@@ -130,18 +130,25 @@ def synthesize(
 
     # 若任务处于 processing 状态（异步模式），触发 Celery 后台轮询
     if job.status.value == "processing":
-        task_id = (job.metadata or {}).get("cosyvoice_task_id", "")
-        if task_id:
-            try:
+        # 分段合成任务 vs 普通单段任务
+        segment_task_ids = (job.metadata or {}).get("segment_task_ids", [])
+        is_segment = len(segment_task_ids) > 0
+
+        try:
+            if is_segment:
+                from worker_app.tasks import process_tts_segment_synthesis
+
+                process_tts_segment_synthesis.delay(job.id)
+            else:
                 from worker_app.tasks import process_tts_synthesis
 
                 process_tts_synthesis.delay(job.id)
-            except Exception as e:
-                # Celery 调度失败，标记 job 为 failed
-                try:
-                    workflow.process_synthesis_failure(job.id, f"Celery 任务调度失败: {e}")
-                except Exception as inner_e:
-                    logger.error(f"Celery 调度后标记失败时出错: job_id={job.id}, error={inner_e}")
+        except Exception as e:
+            # Celery 调度失败，标记 job 为 failed
+            try:
+                workflow.process_synthesis_failure(job.id, f"Celery 任务调度失败: {e}")
+            except Exception as inner_e:
+                logger.error(f"Celery 调度后标记失败时出错: job_id={job.id}, error={inner_e}")
 
     return TTSSynthesizeResponse(
         job_id=job.id,