fix: clear all database tables on startup

src/database.py

@@ -13,7 +13,7 @@ _local = threading.local()
 
 
 def init_db():
-    """初始化数据库表"""
+    """初始化数据库表，启动时清空邮件处理记录"""
     DB_PATH.parent.mkdir(parents=True, exist_ok=True)
     conn = _get_conn()
     conn.executescript("""
@@ -43,6 +43,9 @@ def init_db():
         CREATE INDEX IF NOT EXISTS idx_processed_status ON processed_emails(status);
         CREATE INDEX IF NOT EXISTS idx_processed_account ON processed_emails(account);
     """)
+    conn.execute("DELETE FROM processed_emails")
+    conn.execute("DELETE FROM email_contexts")
+    conn.execute("DELETE FROM conversations")
     conn.commit()
     logger.info("数据库初始化完成: %s", DB_PATH)