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/services/ai_summary.py

@@ -5,9 +5,11 @@ import httpx
 from app.config import settings
 from app.services.dashboard import get_weekly_report, get_week_range
 from app.services.light_board import get_light_board
+from app.models.ai_summary import AISummary
+from sqlalchemy import select
 from sqlalchemy.ext.asyncio import AsyncSession
 from uuid import UUID
-from datetime import date
+from datetime import date, datetime
 
 
 SUMMARY_SYSTEM_PROMPT = """你是一位经验丰富的政企客户经理团队的周报分析助手。你的分析将被直接提交给支局长作为工作周报的文字摘要。
@@ -141,14 +143,70 @@ def build_summary_prompt(
     return data_block
 
 
+async def get_cached_summary(
+    db: AsyncSession,
+    user_id: UUID,
+    reference_date: date | None = None,
+    period: str = "week",
+) -> dict | None:
+    """Load a previously generated summary for this week/user."""
+    ref = reference_date or date.today()
+    monday, sunday = get_week_range(ref)
+    result = await db.execute(
+        select(AISummary)
+        .where(
+            AISummary.week_start == monday,
+            AISummary.period == period,
+            AISummary.generated_by == user_id,
+        )
+        .order_by(AISummary.created_at.desc())
+        .limit(1)
+    )
+    row = result.scalar()
+    if not row:
+        return None
+    return {
+        "summary": row.summary,
+        "week_start": str(row.week_start),
+        "week_end": str(row.week_end),
+        "period": row.period,
+        "created_at": str(row.created_at),
+        "cached": True,
+    }
+
+
+async def delete_cached_summary(
+    db: AsyncSession,
+    user_id: UUID,
+    reference_date: date | None = None,
+    period: str = "week",
+) -> bool:
+    """Delete a cached summary so it can be regenerated."""
+    ref = reference_date or date.today()
+    monday, sunday = get_week_range(ref)
+    result = await db.execute(
+        select(AISummary).where(
+            AISummary.week_start == monday,
+            AISummary.period == period,
+            AISummary.generated_by == user_id,
+        )
+    )
+    rows = result.scalars().all()
+    for row in rows:
+        await db.delete(row)
+    if rows:
+        await db.commit()
+    return len(rows) > 0
+
+
 async def generate_summary(
     db: AsyncSession,
     user_id: UUID,
     role: str,
     reference_date: date | None = None,
     period: str = "week",
-) -> str:
-    """Generate an AI-powered weekly summary.
+) -> dict:
+    """Generate an AI-powered weekly summary, save to DB, return it.
 
     Raises ValueError if AI config is missing, httpx.HTTPError on API failure.
     """
@@ -157,6 +215,7 @@ async def generate_summary(
 
     # Gather data
     ref = reference_date or date.today()
+    monday, sunday = get_week_range(ref)
     weekly_report = await get_weekly_report(
         db=db, user_id=user_id, role=role, reference_date=ref,
     )
@@ -187,4 +246,24 @@ async def generate_summary(
     if not content:
         raise ValueError("AI returned empty response")
 
-    return content
+    # Delete old cached entry for this week/user, then save new
+    await delete_cached_summary(db, user_id, reference_date=ref, period=period)
+    row = AISummary(
+        week_start=monday,
+        week_end=sunday,
+        period=period,
+        generated_by=user_id,
+        role=role,
+        summary=content,
+    )
+    db.add(row)
+    await db.commit()
+
+    return {
+        "summary": content,
+        "week_start": str(monday),
+        "week_end": str(sunday),
+        "period": period,
+        "created_at": str(row.created_at),
+        "cached": False,
+    }