fix(mail): sync Object error, MIME subject decoding, sticky compact pagination

- Fix sync error: backend returns {synced, error?} not {success, synced_count}; frontend now checks error field
- Decode MIME encoded-words (=?UTF-8?Q?...?=) in backend during IMAP sync for subject/from/to/cc headers
- Add frontend decodeMimeHeader() utility for already-stored encoded subjects (MailList + MailDetail)
- Make pagination sticky at bottom of mail list (flex-col h-full, ul scrolls, pagination flex-shrink-0)
- Make pagination compact: smaller padding (px-1.5 py-0.5), text-xs, smaller icons, tighter spacing

app/plugins/builtins/mail/services.py

@@ -707,11 +707,22 @@ async def imap_sync_account(
                             else:
                                 body_text = decoded
 
+                    from email.header import decode_header, make_header
+
+                    def _decode_mime_header(value: str) -> str:
+                        """Decode MIME encoded-words (=?UTF-8?Q?...?=) to readable text."""
+                        if not value:
+                            return ""
+                        try:
+                            return str(make_header(decode_header(value)))
+                        except Exception:
+                            return value
+
                     message_id = msg.get("Message-ID", make_msgid())
-                    subject = msg.get("Subject", "")
-                    from_addr = msg.get("From", "")
-                    to_addrs = msg.get("To", "")
-                    cc_addrs = msg.get("Cc", "")
+                    subject = _decode_mime_header(msg.get("Subject", ""))
+                    from_addr = _decode_mime_header(msg.get("From", ""))
+                    to_addrs = _decode_mime_header(msg.get("To", ""))
+                    cc_addrs = _decode_mime_header(msg.get("Cc", ""))
                     refs = msg.get("References", "")
                     in_reply_to = msg.get("In-Reply-To")
                     date_str = msg.get("Date", "")