Fix silent failures and false success pings

- Collapse folded Message-ID headers before IMAP SEARCH; embedded
  CRLF was breaking the command and crashing every run
- Set Type=oneshot so the success ping only fires on clean exit
  instead of on every spawn, letting OnFailure report real failures

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

email_forwarder/email_forwarder.py

@@ -197,6 +197,9 @@ class EmailForwarder:
             msg_id = msg.get("Message-ID")
             if not msg_id:
                 continue
+            # Collapse folded headers (embedded CRLF/whitespace) so the
+            # Message-ID is safe to embed in an IMAP SEARCH command.
+            msg_id = "".join(msg_id.split())
             if msg_id in self.processed_ids:
                 continue
             self.dest.ensure_folder_exists(folder)