Reshape the app-only suppression marker to a group/app polymorphic owner
(mirrors 0056/0057 + the 0051/0052 config markers): nullable group_id
(CASCADE), nullable app_id, exactly-one CHECK, per-owner partial unique
indexes. Lets a [group] decline a template it inherits from a higher
ancestor for its whole subtree; consumption filters land in M1.3/M1.4.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
