refactor: separate email poll, email process, TG poll into threads

- main.py spawns 3 daemon threads: email poller, email processor, TG poller
- Each thread runs independently so retries don't block other operations
- _pending_uids set + lock prevents duplicate queueing across poll cycles
- summarizer.py split into poll_accounts() (generator) and process_email()
- Graceful shutdown via shared _running flag

src/summarizer.py

@@ -1,43 +1,32 @@
 import logging
+from typing import Generator
 from src.config import Config
-from src.email_client import fetch_unseen_emails, mark_as_seen
+from src.email_client import fetch_unseen_emails, mark_as_seen, Email
 from src.ai_client import summarize_email
 from src.tg_bot import send_summary, format_summary
 
 logger = logging.getLogger(__name__)
 
 
-def process_all(cfg: Config):
+def poll_accounts(cfg: Config) -> Generator[tuple[int, Email], None, None]:
     for idx, acct in enumerate(cfg.email_accounts):
         try:
-            _process_account(cfg, acct, idx)
+            logger.info(f"检查邮箱: {acct.username}")
+            emails = fetch_unseen_emails(acct)
+            if emails:
+                logger.info(f"  发现 {len(emails)} 封新邮件")
+            for mail in emails:
+                yield idx, mail
         except Exception as e:
-            logger.error(f"处理邮箱 {acct.username} 时出错: {e}", exc_info=True)
+            logger.error(f"轮询 {acct.username} 失败: {e}", exc_info=True)
 
 
-def _process_account(cfg: Config, acct, acct_idx: int):
-    logger.info(f"检查邮箱: {acct.username}")
-    emails = fetch_unseen_emails(acct)
-
-    if not emails:
-        logger.info(f"  没有新邮件")
-        return
-
-    logger.info(f"  发现 {len(emails)} 封新邮件")
-    seen_uids = []
-
-    for mail in emails:
-        try:
-            logger.info(f"  正在摘要: {mail.subject}")
-            summary = summarize_email(cfg.ai, acct.username, mail.subject, mail.sender, mail.body)
-            summary["recipient"] = acct.username
-            text = format_summary(summary)
-            send_summary(cfg.telegram, cfg.telegram.chat_id, text, summary, mail.body, acct_idx)
-            seen_uids.append(mail.uid)
-            logger.info(f"  已发送到 Telegram")
-        except Exception as e:
-            logger.error(f"  处理邮件 '{mail.subject}' 失败: {e}", exc_info=True)
-            seen_uids.append(mail.uid)
-
-    if seen_uids:
-        mark_as_seen(acct, seen_uids)
+def process_email(cfg: Config, acct_idx: int, mail: Email):
+    acct = cfg.email_accounts[acct_idx]
+    logger.info(f"  正在摘要: {mail.subject}")
+    summary = summarize_email(cfg.ai, acct.username, mail.subject, mail.sender, mail.body)
+    summary["recipient"] = acct.username
+    text = format_summary(summary)
+    send_summary(cfg.telegram, cfg.telegram.chat_id, text, summary, mail.body, acct_idx)
+    mark_as_seen(acct, [mail.uid])
+    logger.info(f"  已处理: {mail.subject}")