feat(v1.1.1-kv): migrations + KvService trait + Postgres impl

First v1.1.1 commit. Adds the KV store the design notes commit to:
`(app_id, collection, key)` identity with JSONB value and a per-app
index. Trait lives in `picloud-shared` so the executor-core Rhai
bridge (next commit), the Postgres impl, and tests all depend on the
same surface without coupling crates.

The `Services` bundle grows from empty to three fields: `kv`,
`dead_letters` (NoopDeadLetterService stub — replaced by the
Postgres impl in commit 8), and `events` (NoopEventEmitter until the
outbox emitter lands with the dispatcher). Tests use
`Services::default()` for an all-noop bundle.

New capabilities `AppKvRead` / `AppKvWrite` join the Capability
enum. They map onto the existing seven-value `Scope` (script:read /
script:write) — the scope vocabulary stays locked per the
`docs/versioning.md` commitment.

Script-as-gate semantics in `KvServiceImpl`: capability check runs
when `cx.principal.is_some()`, skipped when None (public HTTP).
Cross-app isolation is enforced independently by deriving every
row's `app_id` from `cx.app_id` rather than a script-passed argument.

In-memory `KvRepo` impl + unit tests cover the round-trips, the
cross-app isolation property, empty-collection rejection,
script-as-gate behaviour for both anonymous and authed contexts,
and cursor-style pagination. Postgres impl exists; integration
testing waits for a real DB harness (see HANDBACK).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/manager-core/src/lib.rs

@@ -21,6 +21,8 @@ pub mod auth_api;
 pub mod auth_bootstrap;
 pub mod auth_middleware;
 pub mod authz;
+pub mod kv_repo;
+pub mod kv_service;
 pub mod log_sink;
 pub mod migrations;
 pub mod repo;
@@ -63,6 +65,8 @@ pub use auth_middleware::{
     API_KEY_PREFIX, API_KEY_PREFIX_LEN, SESSION_COOKIE,
 };
 pub use authz::{can, require, AuthzDenied, AuthzError, AuthzRepo, Capability, Decision};
+pub use kv_repo::{KvRepo, KvRepoError, PostgresKvRepo};
+pub use kv_service::KvServiceImpl;
 pub use log_sink::PostgresExecutionLogSink;
 pub use repo::{
     ExecutionLogRepository, NewScript, PostgresExecutionLogRepository, PostgresScriptRepository,