fix: 修复 episodes + yearly_targets 模型导入缺失，增 DELETE 接口，冒烟 6/6 全绿

backend/app/api/episodes.py

@@ -1,5 +1,5 @@
 """
-节目期次 API — 增改查（责编和管理员可操作）
+节目期次 API — 增删改查（责编和管理员可操作）
 """
 
 from fastapi import APIRouter, Depends, HTTPException, status
@@ -7,6 +7,7 @@ from sqlmodel import Session, select
 
 from app.core.deps import get_current_user, require_role
 from app.db.session import get_session
+from app.models.episode import Episode
 from app.models.user import User, UserRole
 from app.schemas.episode import EpisodeCreate, EpisodeResponse, EpisodeUpdate
 
@@ -79,4 +80,19 @@ def update_episode(
     session.add(episode)
     session.commit()
     session.refresh(episode)
-    return episode
+    return episode
+
+
+@router.delete("/{episode_id}", status_code=status.HTTP_204_NO_CONTENT)
+def delete_episode(
+    episode_id: int,
+    session: Session = Depends(get_session),
+    current_user: User = Depends(require_role(UserRole.zhipianren, UserRole.zebian)),
+):
+    """删除一期节目（仅管理员/责编）。"""
+    episode = session.get(Episode, episode_id)
+    if episode is None:
+        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="期次不存在")
+    session.delete(episode)
+    session.commit()
+    return None