Allocate shared project item numbers atomically #80

Work

Implement the #73 reference registry and transactional sequence from the approved contract. Integrate task/subtask creation, memory creation and bulk writes. Enforce uniqueness in the database, keep internal typed IDs, preserve retry/idempotency behavior and retain allocated numbers permanently.

Acceptance

• Concurrent memory/task/batch creates in one project cannot collide.
• Different projects each have their own sequence.
• Transaction failure and batch replay do not create duplicate items or recycle a visible number.
• Verify SQL Server behavior and the SQLite test path; a process-local lock is insufficient.

Dependencies

The contract/migration specification under #73.