Describe the bug

In fetcher/fetcher.go:1045-1046, the debug log file is opened and closed inline without defer:

_, _ = f.WriteString(msg)
_ = f.Close()

If a panic occurs between open and close (or if WriteString panics), the file descriptor leaks.

To reproduce

1. Enable DEBUG_IMAP
2. Trigger a panic during IMAP logging
3. File descriptor leaked

Expected behavior

Use defer f.Close() immediately after opening the file.