Schema groundwork for the trigger `name` identity (the manifest merge key
that will let `apply` Update a trigger in place rather than only
Create/Delete). A `gen_random_uuid()` default keeps the existing write
paths valid and unique without code changes; existing rows are backfilled
to the readable `{kind}-{n}` form; `UNIQUE(app_id, name)` is enforced.
No behavior change yet — the manager-core write paths and the apply diff
start using the name in the follow-up. Verified the migration applies and
the trigger journeys (which create triggers via the unnamed path → default
name) stay green.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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