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>

crates/manager-core/src/lib.rs

@@ -60,6 +60,8 @@ pub mod group_kv_repo;
 pub mod group_kv_service;
 pub mod group_members_repo;
 pub mod group_pubsub_service;
+pub mod group_queue_repo;
+pub mod group_queue_service;
 pub mod group_quota;
 pub mod group_repo;
 pub mod group_scripts_api;
@@ -200,6 +202,10 @@ pub use group_members_repo::{
     PostgresGroupMembersRepository,
 };
 pub use group_pubsub_service::GroupPubsubServiceImpl;
+pub use group_queue_repo::{
+    GroupQueueRepo, GroupQueueRepoError, NewGroupQueueMessage, PostgresGroupQueueRepo,
+};
+pub use group_queue_service::GroupQueueServiceImpl;
 pub use group_repo::{
     GroupChildCounts, GroupRepository, GroupRepositoryError, PostgresGroupRepository,
     ROOT_GROUP_SLUG,