Add tooltips to Accept, Reject, Discard buttons in held messages view

Signed-off-by: itvi-1234 rjsumit71@gmail.com

Add descriptive Bootstrap tooltips to all six moderation buttons in the held messages view — the three in the bulk action bar and the three in the per-message modal footer. Tooltip text clearly explains what each action does:

- Accept: Deliver the message(s) to the list.

- Reject: Discard and send a rejection notice to the sender(s).

- Discard: Silently delete without notifying the sender(s).

Tooltips are initialized using the Bootstrap 5 Tooltip API already available on the page. Modal buttons are re-initialized on the 'shown.bs.modal' event .Orphaned tooltip popups are cleaned up on the 'hide.bs.modal' event."

Closes #551