feat(modules): GroupKvService + kv::shared SDK handle (§11.6 C3)

The runtime for shared group collections. A script reaches a shared store via
the explicit kv::shared("name") handle (distinct GroupKvHandle Rhai type, so
private-vs-shared scope is a deliberate choice). The service resolves the
owning group from cx.app_id's ancestor chain — the script never names a group,
and that walk is the isolation boundary (a foreign app's chain never contains
the owning group → CollectionNotShared).

- shared: GroupKvService trait + GroupKvError + NoopGroupKvService; threaded
  into the Services bundle as a field defaulted to noop, opted into via a new
  with_group_kv() (keeps the ~14 Services::new call sites unchanged).
- manager-core: GroupKvServiceImpl with the reads-open/writes-authed split —
  reads use script_gate (anonymous public scripts skip), writes use the new
  script_gate_require_principal (anonymous fails closed). Owner resolution
  behind a GroupCollectionResolver trait (Postgres impl + injectable fake);
  unit tests cover off-chain CollectionNotShared, anonymous-read-OK/
  anonymous-write-Forbidden, authed-no-role-Forbidden.
- executor-core: GroupKvHandle + kv::shared constructor + get/set/has/delete/
  list (Rhai dispatches by receiver type, reusing the block_on bridge).
- picloud: wire PostgresGroupKvRepo + resolver + GroupKvServiceImpl.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/manager-core/src/lib.rs

@@ -52,6 +52,7 @@ pub mod files_sweep;
 pub mod gc;
 pub mod group_collection_repo;
 pub mod group_kv_repo;
+pub mod group_kv_service;
 pub mod group_members_repo;
 pub mod group_repo;
 pub mod group_scripts_api;
@@ -178,6 +179,10 @@ pub use files_repo::{FilesConfig, FilesRepo, FilesRepoError, FsFilesRepo};
 pub use files_service::FilesServiceImpl;
 pub use files_sweep::{spawn_files_orphan_sweep, sweep_orphan_tmp_files, SweepStats};
 pub use gc::{spawn_abandoned_gc, spawn_app_user_token_gc, spawn_dead_letter_gc};
+pub use group_kv_repo::{GroupKvRepo, GroupKvRepoError, PostgresGroupKvRepo};
+pub use group_kv_service::{
+    GroupCollectionResolver, GroupKvServiceImpl, PostgresGroupCollectionResolver,
+};
 pub use group_members_repo::{
     GroupMembersRepository, GroupMembersRepositoryError, GroupMembershipDetail, GroupMembershipRow,
     PostgresGroupMembersRepository,
@@ -190,7 +195,6 @@ pub use group_scripts_api::{group_scripts_router, GroupScriptsApiError, GroupScr
 pub use groups_api::{groups_router, GroupsApiError, GroupsState};
 pub use http_service::{HttpConfig, HttpServiceImpl};
 pub use kv_api::{kv_admin_router, KvAdminState};
-pub use group_kv_repo::{GroupKvRepo, GroupKvRepoError, PostgresGroupKvRepo};
 pub use kv_repo::{KvRepo, KvRepoError, PostgresKvRepo};
 pub use kv_service::KvServiceImpl;
 pub use log_sink::PostgresExecutionLogSink;