test: Phase 3 添加 smoke test、CI 与 run-daily 去重锁

离线 mock 测试 generate 产出，GitHub Actions 跑 pytest，30 分钟内重复调度自动 skip。

Co-authored-by: Cursor <cursoragent@cursor.com>

tests/fixtures/sample-rss.xml

@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<rss version="2.0">
+  <channel>
+    <title>Sample AI Feed</title>
+    <item>
+      <title>Sample AI headline for smoke tests</title>
+      <link>https://example.com/ai-news/1</link>
+      <pubDate>Wed, 02 Jul 2026 08:00:00 GMT</pubDate>
+      <description>A minimal RSS item used by offline tests.</description>
+    </item>
+  </channel>
+</rss>