Drawing set — sheet index, revisions, and "issued for" snapshots

The Drawings tab is per-sheet version control plus issued-set snapshots.

Workflow:
1. **Add sheets** to the index — sheet number (A-101), title (First Floor Plan), discipline (architectural, structural, etc.). The index sorts automatically by discipline + sheet number.
2. **Upload a PDF revision** for each sheet. The first upload becomes rev 1; subsequent uploads bump the rev counter. Every revision is preserved in storage — the index just tracks the current rev.
3. **Issue a set** when you're ready to share with the contractor — pick a purpose (Issued for Review / Permit / Bid / Construction / As-Built). The set is a frozen snapshot of the current rev of every sheet at that moment.
4. Future edits don't change a frozen set. If you re-issue, that's a new set with a new snapshot.

The linked BuildOS contractor sees both the current sheet index (always live) and the issued sets (frozen reference points like "what we bid against" or "what we built from").