[BGM-PR-13] Oracle Repository Transitions

[slin1237]

Parent: #1214

Track: Oracle
Suggested milestone group: Slice C

Goal

Implement the Oracle repository with the same semantics as Postgres.

Acceptance Criteria

• Oracle implements enqueue, claim, cancel, finalize, delete, stream append/load, and lease requeue.
• Claim uses an ordered cursor with FOR UPDATE SKIP LOCKED and does not rely on the forbidden FETCH FIRST ... FOR UPDATE SKIP LOCKED combination.
• Lock ordering matches the design.
• Repository tests cover the same transition matrix as Postgres where Oracle can support it deterministically.

Dependencies

• [BGM-PR-02] Background Repository Trait, Schema, and Migrations #1216

Out of Scope

• Oracle scheduler loop.
• Oracle resume tailing.