feat(v1.1.1-kv): Rhai kv:: SDK module + ctx.event wiring

Wires the KV store into Rhai scripts via the handle pattern:

    let widgets = kv::collection("widgets");
    widgets.set("k", #{ n: 1 });
    let v = widgets.get("k");          // value or () if absent
    widgets.has("k") / widgets.delete("k")
    let page = widgets.list();          // cursor-style pagination

`KvHandle` is a custom Rhai type holding `Arc<dyn KvService>` + the
per-call `Arc<SdkCallCx>`. Methods route async service calls through
`tokio::Handle::current().block_on(...)` — works because
`LocalExecutorClient` runs the script under `spawn_blocking` so a
runtime is reachable. The bridge surfaces `app_id` exclusively
through `cx.app_id`; no public-facing argument can spoof an app.

`TriggerEvent` lands in `picloud-shared` as the wire shape the
dispatcher will emit (KV + DeadLetter variants — KV exercised now,
DL hooks up with the dispatcher in commit 5/8). `SdkCallCx` and
`ExecRequest` grow `is_dead_letter_handler: bool` and
`event: Option<TriggerEvent>`. `engine.rs::build_ctx_map` flattens
the event into `ctx.event` for triggered handlers; direct ingress
leaves the key absent so scripts can `if "event" in ctx`.

Tests:
- 7 `sdk_kv.rs` integration tests covering the full Rhai surface
  (round-trip, missing-key unit, has bool, delete was-present,
  empty-collection rejection, cursor pagination, cross-app
  isolation through the bridge).
- 3 new `engine.rs` tests pinning `ctx.event` shape per
  design notes §4 (KV insert with value, delete with unit value,
  direct invocations have no `event` key).

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

crates/executor-core/src/sdk/mod.rs

@@ -13,6 +13,7 @@
 
 pub mod bridge;
 pub mod cx;
+pub mod kv;
 pub mod stdlib;
 
 pub use bridge::{dynamic_to_json, json_to_dynamic};
@@ -27,14 +28,10 @@ use rhai::Engine as RhaiEngine;
 /// once per invocation, just after `build_engine` constructs the
 /// sandboxed Rhai engine and just before script compilation.
 ///
-/// v1.1.0 ships an intentionally empty body — the call site exists so
-/// future PRs (KV first) drop their registration logic here rather
-/// than reaching into `engine.rs::build_engine`. The signature is
-/// locked: subsequent PRs MUST keep the same parameter shape so that
-/// hosts don't have to re-thread the plumbing.
+/// v1.1.1 wires the first stateful service (KV). Subsequent PRs add a
+/// single `<service>::register(...)` line per service.
 pub fn register_all(engine: &mut RhaiEngine, services: &Services, cx: Arc<SdkCallCx>) {
-    // Intentionally inert in v1.1.0. The unused-suppression below is a
-    // load-bearing placeholder: future PRs replace this `let _` with
-    // real `register_kv(engine, services, cx.clone())` calls etc.
-    let _ = (engine, services, cx);
+    kv::register(engine, services, cx.clone());
+    // v1.1.1 commit 8: dead_letters::register(engine, services, cx.clone());
+    let _ = cx;
 }