feat(news): research 时讯加可信过滤、去重与国内配额

候选池按独立事件拉取，白名单过滤低质源，同事件与 tech 主题去重后按展示上限打包。

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

tests/test_ai_news_research.py

@@ -5,7 +5,24 @@ from __future__ import annotations
 import unittest
 
 from daily.format_wecom import _ai_news_lines, replace_wecom_news_sections
-from daily.news.research import parse_research_response
+from daily.news.research import (
+    parse_research_response,
+    research_pool_limit,
+    research_tech_pool_limit,
+)
+
+
+class TestAiNewsResearchPool(unittest.TestCase):
+    def test_pool_defaults_above_display(self):
+        self.assertEqual(research_pool_limit(10), 20)
+        self.assertEqual(research_tech_pool_limit(5), 10)
+
+    def test_pool_env_override(self):
+        import os
+        from unittest import mock
+
+        with mock.patch.dict(os.environ, {"DAILY_AI_NEWS_RESEARCH_POOL": "24"}, clear=False):
+            self.assertEqual(research_pool_limit(10), 24)
 
 
 class TestAiNewsResearchParse(unittest.TestCase):