fix(#1197): 修复AI Code Review阻塞级问题

1. 预览分辨率按video_ratio动态计算（支持9:16竖屏/1:1/4:3等）
2. 入队失败时标记任务为failed，避免僵尸pending数据

apps/api/app/api/routes/generation_preview.py

@@ -39,6 +39,30 @@ router = APIRouter()
 PREVIEW_RESOLUTION = "854x480"
 
 
+def _calc_preview_resolution(video_ratio: str = "") -> str:
+    """根据视频比例计算预览分辨率（短边 480，长边按比例）。
+
+    支持的比例：16:9, 9:16, 1:1, 4:3, 3:4, 其他默认 16:9。
+    """
+    ratio_map = {
+        "16:9": "854x480",
+        "9:16": "480x854",
+        "1:1": "480x480",
+        "4:3": "640x480",
+        "3:4": "480x640",
+    }
+    return ratio_map.get(video_ratio.strip(), PREVIEW_RESOLUTION)
+
+
+def _mark_task_failed(repo, task, reason: str) -> None:
+    """入队失败时将任务标记为 failed，避免产生僵尸 pending 数据。"""
+    try:
+        task.mark_failed(error_message=f"入队失败：{reason}")
+        repo.update(task)
+    except Exception:
+        logger.exception("[预览生成] 标记任务失败时异常: task_id=%s", task.id)
+
+
 def _to_preview_response(task, generated_videos: list | None = None) -> PreviewGenerationTaskResponse:
     """将领域任务对象转换为预览响应 DTO。
 
@@ -152,7 +176,7 @@ def create_preview_generation_task(
                 asset_select_mode="",
                 batch_id="",
                 video_title=request.video_title,
-                resolution=PREVIEW_RESOLUTION,
+                resolution=_calc_preview_resolution(request.video_ratio),
                 bgm_config=request.bgm_config or {},
                 auto_retry_enabled=False,
                 auto_retry_max=0,
@@ -166,7 +190,7 @@ def create_preview_generation_task(
         logger.error("[预览生成] 创建失败: %s", e, exc_info=True)
         raise HTTPException(status_code=500, detail="创建预览生成任务失败，请稍后重试") from e
 
-    # 入队执行
+    # 入队执行；若入队失败则标记任务为 failed 避免僵尸数据
     try:
         if not safe_enqueue_generation_task(
             task,
@@ -176,13 +200,16 @@ def create_preview_generation_task(
             log_task_status=True,
         ):
             logger.warning("[预览生成] 任务入队失败: task_id=%s", task.id)
+            _mark_task_failed(generation_task_repository, task, "任务入队失败")
             raise HTTPException(status_code=500, detail="任务入队失败，请稍后重试")
     except UserPendingLimitExceeded:
+        _mark_task_failed(generation_task_repository, task, "待处理任务超限")
         raise HTTPException(
             status_code=429,
             detail="您的待处理任务过多，请等待完成后再提交",
         ) from None
     except GlobalQueueFull:
+        _mark_task_failed(generation_task_repository, task, "系统队列已满")
         raise HTTPException(
             status_code=503,
             detail="系统繁忙，请稍后再试",