fix: increment revision on updateMarks to preserve CAS invariant

[tmchow]

Bug

updateMarks in server/db.ts updated marks and updated_at but never incremented revision:

-- before
SET marks = ?, updated_at = ?

-- after
SET marks = ?, updated_at = ?, revision = revision + 1

Every other write path (updateDocumentAtomic, updateDocumentAtomicByRevision) increments revision. updateMarks did not.

Impact

The edit/v2 endpoint uses baseRevision as a CAS lock via updateDocumentAtomicByRevision. Because marks mutations left revision unchanged, an agent could:

1. Read the document at revision = N
2. A marks mutation fires — document still at revision = N
3. Agent calls edit/v2 with baseRevision = N — CAS check passes on a stale base
4. Agent write silently clobbers the mark anchors

Fix

Added revision = revision + 1 to the updateMarks SQL in server/db.ts, consistent with all other write paths.