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/orchestrator-core/src/api.rs

@@ -317,6 +317,11 @@ fn build_exec_request(
         // preserves the original root for chained executions.
         trigger_depth: 0,
         root_execution_id: execution_id,
+        // Direct invocations are never DL handlers — that flag is only
+        // set by the dispatcher when it picks a dead_letter trigger row.
+        is_dead_letter_handler: false,
+        // No originating trigger event for direct ingress.
+        event: None,
     })
 }