Thunderbird mbox: tail-slice the file before parsing it with Python

To search a huge Thunderbird IMAP mbox cache (2 GB+) with Python's mailbox.mbox, take only the end with tail -c 300000000 INBOX, drop the bytes before the first '\nFrom ' line, and parse that slice; it takes seconds instead of minutes. Write the slice to an explicit absolute path. With cmd > "$TMPDIR/x" || cmd > other, the fallback never runs once the first redirect succeeds, and later steps that read the other path see an empty file. Online-class Zoom links usually aren't in email: Canvas notifications only say 'use Zoom on the Canvas page', so point the user to the course's Zoom tool at canvas/courses/<id> instead of hunting for a zoom.us link.