concurrency advisory lock key is not queue-scoped

[maxcountryman]

Summary

Advisory lock key derivation uses raw concurrency_key (or task id string) without queue namespace.

Why this is a problem

Different queues using the same concurrency key can unintentionally contend on the same advisory lock, causing cross-queue interference.

Evidence

• Lock key returns only concurrency_key or task_id: src/queue.rs:1797
• Lock acquisition hashes that single key globally: src/queue.rs:1811

Expected behavior

Concurrency controls should be isolated per queue unless global coordination is intentionally requested.

Proposed direction

• Namespace lock key with queue name (e.g. "{queue}:{key}").
• Optionally support explicit global key mode separately.

Acceptance criteria

• Two tasks in different queues with same concurrency key do not block each other by default.