feat: 深色主题UI、错误分类、批量抓取、健康度筛选

- 修复 datetime 时区不一致导致所有API 500错误的问题
- Feeds/Dashboard 页面改为深色表格主题，高对比度文字
- 添加错误类型自动分类（URL失效/被拒绝/超时/DNS失败/SSL错误等12种）
- 新增"下次抓取时间"列，从APScheduler获取
- 新增健康度筛选下拉，修复分页后过滤失效的bug
- "全部抓取"改为同步并发执行，基于当前筛选条件获取所有匹配源
- 新增数据库自动迁移机制，处理增量列变更

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

backend/rss_fetcher.py

@@ -2,7 +2,7 @@
 import time
 import re
 import html
-from datetime import datetime, timezone
+from datetime import datetime
 from concurrent.futures import ThreadPoolExecutor, as_completed
 from urllib.parse import urljoin
 import requests
@@ -14,6 +14,39 @@ from database import SessionLocal
 import config
 
 
+def classify_error(error: str) -> str:
+    """根据错误信息分类错误类型"""
+    if not error:
+        return ""
+    err = error.lower()
+
+    if "404" in error or "not found" in err:
+        return "url_invalid"
+    if "403" in error or "forbidden" in err:
+        return "forbidden"
+    if "429" in error or "too many request" in err:
+        return "rate_limited"
+    if "timeout" in err or "timed out" in err:
+        return "timeout"
+    if "connecttimeout" in err or "connectiontimeout" in err:
+        return "timeout"
+    if "could not resolve" in err or "name or service not known" in err or "nodename nor servname" in err:
+        return "dns_failure"
+    if "connection refused" in err:
+        return "connection_refused"
+    if "connection aborted" in err or "remotedisconnected" in err or "remote end closed" in err:
+        return "connection_reset"
+    if "ssl" in err or "certificate" in err or "certifi" in err:
+        return "ssl_error"
+    if "max retries" in err or "newconnectionerror" in err:
+        return "unreachable"
+    if "invalid url" in err or "no host" in err or "missing scheme" in err:
+        return "url_malformed"
+    if "5" in error and "server error" in err:
+        return "server_error"
+    return "unknown"
+
+
 def fetch_feed(url: str, timeout: int = config.FETCH_TIMEOUT) -> dict:
     """抓取单个 RSS 源
     返回 {"success": bool, "feed_data": parsed, "error": str, "response_time_ms": int}
@@ -102,12 +135,12 @@ def parse_article(entry, feed_id: int) -> dict:
     published_at = None
     if hasattr(entry, "published_parsed") and entry.published_parsed:
         try:
-            published_at = datetime(*entry.published_parsed[:6], tzinfo=timezone.utc)
+            published_at = datetime(*entry.published_parsed[:6])
         except (ValueError, TypeError):
             pass
     if not published_at and hasattr(entry, "updated_parsed") and entry.updated_parsed:
         try:
-            published_at = datetime(*entry.updated_parsed[:6], tzinfo=timezone.utc)
+            published_at = datetime(*entry.updated_parsed[:6])
         except (ValueError, TypeError):
             pass
 
@@ -199,9 +232,10 @@ def fetch_and_store_feed(feed_id: int) -> dict:
 
         if not result["success"]:
             # 记录失败
-            feed.last_fetch_at = datetime.now(timezone.utc)
+            feed.last_fetch_at = datetime.utcnow()
             feed.last_fetch_status = "fail"
             feed.last_error = result["error"]
+            feed.error_type = classify_error(result["error"])
             feed.fail_count += 1
 
             log = FetchLog(
@@ -264,9 +298,10 @@ def fetch_and_store_feed(feed_id: int) -> dict:
                         existing.published_at = article_data["published_at"]
 
         # 更新 feed 统计
-        feed.last_fetch_at = datetime.now(timezone.utc)
+        feed.last_fetch_at = datetime.utcnow()
         feed.last_fetch_status = "success"
         feed.last_error = ""
+        feed.error_type = ""
         feed.success_count += 1
         feed.article_count += new_count