feat: AI 摘要持久化 — DB 缓存 + 自动加载

后端:
- 新增 ai_summaries 表 (week_start/week_end/generated_by/summary)
- get_cached_summary(): 按周+用户查缓存
- delete_cached_summary(): 生成前清理旧缓存
- generate_summary(): 自动保存到 DB
- API: GET /ai/summary(加载) POST(生成) DELETE(清除)

前端:
- onMounted 自动 GET 缓存摘要, 有则直接展示
- 按钮: 无缓存→'AI 生成摘要', 有缓存→'重新生成'
- 标题栏显示生成时间戳

backend/app/api/ai_summary.py

@@ -1,4 +1,4 @@
-"""AI summary endpoints — LLM-powered weekly report narrative."""
+"""AI summary endpoints — LLM-powered weekly report narrative with caching."""
 
 import uuid
 from datetime import date
@@ -7,34 +7,68 @@ from fastapi import APIRouter, Depends, Query, HTTPException
 from sqlalchemy.ext.asyncio import AsyncSession
 from app.database import get_db
 from app.middleware.auth import get_current_user
-from app.services.ai_summary import generate_summary
+from app.services.ai_summary import generate_summary, get_cached_summary, delete_cached_summary
 
 router = APIRouter(prefix="/ai", tags=["AI Summary"])
 
 
-@router.post("/summary")
-async def ai_summary(
+def _check_role(role: str):
+    if role not in ("director", "leader"):
+        raise HTTPException(status_code=403, detail="仅限支局长和分管领导使用")
+
+
+def _parse_ref(reference_date: Optional[str]) -> date | None:
+    return date.fromisoformat(reference_date) if reference_date else None
+
+
+@router.get("/summary")
+async def get_summary(
     reference_date: Optional[str] = Query(None),
     period: str = Query("week", regex="^(week|month)$"),
     current_user: dict = Depends(get_current_user),
     db: AsyncSession = Depends(get_db),
 ):
-    """Generate AI-powered weekly report summary. Director/leader only."""
-    role = current_user["role"]
-    if role not in ("director", "leader"):
-        raise HTTPException(status_code=403, detail="仅限支局长和分管领导使用")
+    """Get cached AI summary for this week. Returns null if none exists."""
+    _check_role(current_user["role"])
+    cached = await get_cached_summary(
+        db, uuid.UUID(current_user["user_id"]), _parse_ref(reference_date), period,
+    )
+    return cached or {"summary": None}
 
+
+@router.post("/summary")
+async def create_summary(
+    reference_date: Optional[str] = Query(None),
+    period: str = Query("week", regex="^(week|month)$"),
+    current_user: dict = Depends(get_current_user),
+    db: AsyncSession = Depends(get_db),
+):
+    """Generate (or regenerate) AI summary. Saves to DB automatically."""
+    _check_role(current_user["role"])
     try:
-        ref = date.fromisoformat(reference_date) if reference_date else None
-        summary = await generate_summary(
+        return await generate_summary(
             db=db,
             user_id=uuid.UUID(current_user["user_id"]),
-            role=role,
-            reference_date=ref,
+            role=current_user["role"],
+            reference_date=_parse_ref(reference_date),
             period=period,
         )
-        return {"summary": summary, "period": period, "reference_date": str(ref or date.today())}
     except ValueError as e:
         raise HTTPException(status_code=400, detail=str(e))
     except Exception as e:
         raise HTTPException(status_code=500, detail=f"AI 摘要生成失败：{str(e)}")
+
+
+@router.delete("/summary")
+async def delete_summary(
+    reference_date: Optional[str] = Query(None),
+    period: str = Query("week", regex="^(week|month)$"),
+    current_user: dict = Depends(get_current_user),
+    db: AsyncSession = Depends(get_db),
+):
+    """Delete cached summary so it can be regenerated fresh."""
+    _check_role(current_user["role"])
+    deleted = await delete_cached_summary(
+        db, uuid.UUID(current_user["user_id"]), _parse_ref(reference_date), period,
+    )
+    return {"deleted": deleted}