fix: harden 2925 mailbox reuse and forwarded mail parsing

- 合并 PR #169 的核心改动：在复用 2925 邮箱页前恢复 content script ready，并支持 OpenAI bounce 转发地址反解与中文日期解析。
- 本地补充修复：无。
- 影响范围：2925 邮箱会话确认、2925 邮件轮询、相关回归测试。

tests/background-mail2925-entry-behavior.test.js

@@ -68,7 +68,7 @@ test('ensureMail2925MailboxSession reuses current mailbox page without sending l
   });
 
   assert.equal(sendCalls, 0);
-  assert.equal(readyCalls, 0);
+  assert.equal(readyCalls, 1);
   assert.equal(result.result.usedExistingSession, true);
 });
 

tests/mail-2925-content.test.js

@@ -319,6 +319,7 @@ return {
 test('handlePollEmail skips explicit mismatched target emails when receive-mode matching is enabled', async () => {
   const bundle = [
     extractFunction('extractEmails'),
+    extractFunction('extractForwardedTargetEmails'),
     extractFunction('emailMatchesTarget'),
     extractFunction('getTargetEmailMatchState'),
     extractFunction('normalizeMinuteTimestamp'),