feat(search): 智能搜索建议 - 固化候选词表 (search_keywords + search_title_suggestions)

后端:
- alembic 0009: 两张固化表 + GIN prefix_keys 索引 + articles trigger
- /api/v1/search/suggestions: 混合 A(高频词 ts_stat) + B(真实标题) + 冷启动 fallback
- worker 每日 03:00 + 启动时刷新 search_keywords
- 顺便填 commit 11 TODO: articles.title_zh_tsv + GIN 索引(未来 FTS 基础)

前端:
- NInput -> NAutoComplete + debounce 250ms
- 选标题 -> 跳详情;选关键词 -> 填入 + 触发搜索
- AbortController 防 race condition

性能: prefix_keys @> ARRAY[prefix] 走 GIN 亚毫秒,100w 行也稳

backend/app/workers/__main__.py

@@ -7,13 +7,13 @@ from __future__ import annotations
 import asyncio
 import logging
 import signal
-from datetime import datetime, timezone
+from datetime import datetime, timedelta, timezone
 
 from apscheduler.schedulers.asyncio import AsyncIOScheduler
 from apscheduler.triggers.cron import CronTrigger
 from apscheduler.triggers.date import DateTrigger
 from apscheduler.triggers.interval import IntervalTrigger
-from sqlalchemy import select
+from sqlalchemy import select, text
 
 from app.config import settings
 from app.database import AsyncSessionLocal
@@ -28,6 +28,22 @@ logging.basicConfig(
 )
 
 
+async def _refresh_search_keywords() -> None:
+    """每日刷新 search_keywords(ts_stat 词频表)。
+
+    - 调用 PG 函数 refresh_search_keywords()(迁移 0009 创建)
+    - 全量 truncate + insert,词频会变,不适合增量
+    - 失败也不应阻塞 worker,只记 log
+    """
+    try:
+        async with AsyncSessionLocal() as s:
+            await s.execute(text("SELECT refresh_search_keywords()"))
+            await s.commit()
+        logger.info("search_keywords refreshed")
+    except Exception as e:
+        logger.exception("search_keywords refresh failed: %s", e)
+
+
 async def _rebuild_jobs(scheduler: AsyncIOScheduler) -> None:
     """从 sources 表动态构建 job(可热更新)。
 
@@ -95,6 +111,23 @@ async def main() -> None:
         id="startup_run",
     )
 
+    # === 搜索建议相关 ===
+    # 每日凌晨 03:00 刷新 search_keywords(ts_stat 词频)
+    scheduler.add_job(
+        _refresh_search_keywords,
+        trigger=CronTrigger(hour=3, minute=0),
+        id="refresh_search_keywords",
+        replace_existing=True,
+    )
+    # 启动时延迟 10 秒跑一次(冷启动友好,worker 起来时 search_keywords 就有数据;
+    # 延迟是等 DB 完全就绪 + 不和 startup_run 抢资源)
+    scheduler.add_job(
+        _refresh_search_keywords,
+        trigger=DateTrigger(run_date=datetime.now() + timedelta(seconds=10)),
+        id="startup_refresh_search_keywords",
+    )
+    logger.info("scheduled: refresh_search_keywords daily 03:00 + on startup (+10s)")
+
     scheduler.start()
     logger.info("scheduler started with %d jobs", len(scheduler.get_jobs()))