Tranche 3 of LST-65. Task and Project adopt TimestampableBlamableTrait.
- Additive migration on task and project: created_at/updated_at (nullable),
created_by/updated_by (nullable INT, FK to "user" ON DELETE SET NULL) +
indexes + COMMENT ON COLUMN. down() drops only the added objects.
- Trait fields stay out of the existing API groups (trait carries its own).
- Functional test (TaskTimestampableTest) confirms created_at on persist and
updated_at refresh on update.
161 tests green, no destructive migration.
Matthieu