feat: 代理支持、外部API增强、调度器修复、每日文章看板

- 添加 HTTP 代理支持（国内直连、外网走代理）
- 外部 API 新增全文搜索、源健康度/错误筛选、未读筛选
- 修复 APScheduler 线程静默崩溃（_safe_fetch 异常保护）
- 健康检查暴露调度器状态
- Dashboard 新增每日文章数柱状图（按 published_at）
- 文章列表 API 补上 content 字段，日期筛选修复时间范围
- 修复外部 API 双重 external 前缀
- User-Agent 改为 Chrome 标识缓解 403
- 添加完整 API 接口文档

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend/scheduler.py

@@ -1,9 +1,12 @@
 """APScheduler 定时任务管理"""
+import logging
 from apscheduler.schedulers.background import BackgroundScheduler
 from apscheduler.triggers.interval import IntervalTrigger
 from rss_fetcher import fetch_and_store_feed
 import config
 
+logger = logging.getLogger(__name__)
+
 _scheduler = None
 
 
@@ -11,32 +14,42 @@ def get_scheduler():
     """获取或创建调度器实例"""
     global _scheduler
     if _scheduler is None:
-        _scheduler = BackgroundScheduler()
+        _scheduler = BackgroundScheduler(
+            job_defaults={
+                "coalesce": True,
+                "max_instances": 1,
+                "misfire_grace_time": 300,
+            },
+            logger=logger,
+        )
     return _scheduler
 
 
+def _safe_fetch(feed_id: int):
+    """安全包装：防止单个 job 异常导致调度器线程崩溃"""
+    try:
+        fetch_and_store_feed(feed_id)
+    except Exception as e:
+        logger.error(f"调度抓取失败 feed_id={feed_id}: {e}")
+
+
 def add_feed_job(feed_id: int, interval_minutes: int):
     """为指定 RSS 源添加定时抓取任务"""
     scheduler = get_scheduler()
     job_id = f"fetch_feed_{feed_id}"
-
-    # 确保间隔不低于最小值
     interval = max(interval_minutes, config.MIN_FETCH_INTERVAL)
 
-    # 如果任务已存在则更新
     existing = scheduler.get_job(job_id)
     if existing:
         existing.reschedule(trigger=IntervalTrigger(minutes=interval))
         return
 
     scheduler.add_job(
-        fetch_and_store_feed,
+        _safe_fetch,
         trigger=IntervalTrigger(minutes=interval),
         id=job_id,
         args=[feed_id],
         replace_existing=True,
-        misfire_grace_time=300,  # 5分钟容错
-        coalesce=True,  # 合并错过的任务
     )
 
 
@@ -55,6 +68,7 @@ def start_scheduler():
     scheduler = get_scheduler()
     if not scheduler.running:
         scheduler.start()
+        logger.info("调度器已启动")
 
 
 def stop_scheduler():
@@ -65,6 +79,15 @@ def stop_scheduler():
         _scheduler = None
 
 
+def scheduler_status():
+    """获取调度器状态（供健康检查使用）"""
+    scheduler = get_scheduler()
+    if not scheduler.running:
+        return {"running": False, "jobs": 0}
+    jobs = scheduler.get_jobs()
+    return {"running": True, "jobs": len(jobs)}
+
+
 def get_feed_next_run(feed_id: int):
     """获取指定 RSS 源的下一次抓取时间"""
     scheduler = get_scheduler()
@@ -81,3 +104,4 @@ def init_feed_jobs(db):
     for feed in feeds:
         add_feed_job(feed.id, feed.fetch_interval_minutes or config.DEFAULT_FETCH_INTERVAL)
     start_scheduler()
+    logger.info(f"已注册 {len(feeds)} 个定时抓取任务")