Migrations 0061 (activity-log task-id index), 0062 (remove task/subtask
splitting), 0063 (AI merge review reconciliation), and 0064 (task repository
scope) advanced SCHEMA_BASELINE_VERSION to 0064 without updating this
non-gate PG integration test, leaving it red on the non-blocking suite:
- Bump the immutable-identity assertion to 0064 and pin 0062-0064 identities.
- Append the four new versions to all five getAppliedMigrations() lists.
- Add central.central_activity_log to the hand-built 0000 upgrade fixture so
the 0061 index migration finds the relation real 0000 DBs have from
0000_initial.sql (fixture gap, not a product regression).
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