i18n: translate all Chinese comments, docstrings, and logger messages to English

Comprehensive translation of Chinese text to English across the entire codebase:

- api/: FastAPI server documentation and logger messages
- cache/: Cache abstraction layer comments and docstrings
- database/: Database models and MongoDB store documentation
- media_platform/: All platform crawlers (Bilibili, Douyin, Kuaishou, Tieba, Weibo, Xiaohongshu, Zhihu)
- model/: Data model documentation
- proxy/: Proxy pool and provider documentation
- store/: Data storage layer comments
- tools/: Utility functions and browser automation
- test/: Test file documentation

Preserved: Chinese disclaimer header (lines 10-18) for legal compliance

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

test/test_expiring_local_cache.py

@@ -45,9 +45,9 @@ class TestExpiringLocalCache(unittest.TestCase):
         self.assertIsNone(self.cache.get('key'))
 
     def test_clear(self):
-        # 设置两个键值对，过期时间为11秒
+        # Set two key-value pairs with expiration time of 11 seconds
         self.cache.set('key', 'value', 11)
-        # 睡眠12秒，让cache类的定时任务执行一次
+        # Sleep for 12 seconds to let the cache class's scheduled task execute once
         time.sleep(12)
         self.assertIsNone(self.cache.get('key'))