fix: roll back failed transaction commits

[huytdps13400]

Summary

• replace the ambiguous isFinished flag with explicit transaction finalization states
• mark commits and rollbacks complete only after their SQL succeeds
• allow a failed commit to enter the rollback path
• preserve the original commit error and expose both errors through an AggregateError if rollback also fails
• cover automatic and manual commit failures using deferred foreign-key constraints

Verification

• focused iOS harness RED before fix: both cases retained the invalid child row after COMMIT failed
• focused iOS harness GREEN: 2 passed
• full iOS unit harness: 34 passed
• TypeORM harness: 1 passed
• bun typecheck (all three workspaces)
• bun lint
• repository-wide Prettier check
• git diff --check
• no lockfile changes

Closes #307.