feat(shared-queues): group-keyed queue store + enqueue service + SDK (D3.1)
The producer side of shared durable queues:
- migration 0065 group_queue_messages (mirrors 0034, keyed by (group_id,
collection); CASCADE on group delete).
- GroupQueueRepo/PostgresGroupQueueRepo: enqueue + the competing-consumer
claim (FOR UPDATE SKIP LOCKED) + ack/nack/drop_exhausted/reclaim/depth.
- GroupQueueService trait (shared) + GroupQueueServiceImpl: resolve owning
group (kind='queue') from cx.app_id's chain, require editor+
(GroupQueueEnqueue, fails closed on anon), size-cap, enqueue.
- SDK: `queue::shared_collection("name")` -> GroupQueueHandle with
`.enqueue(msg[, opts])` / `.depth()` / `.depth_pending()`; wired through
Services + the picloud binary.
- authz: Capability::GroupQueueEnqueue(GroupId), editor+ / script:write.
Deterministic test proves competing consumers claim each message exactly
once. Consumption wiring (materialized consumers + dispatcher branch) lands
in D3.2.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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