feat(shared): SdkCallCx, Services bundle, ServiceEventEmitter trait shape

Foundation for the v1.1.x stateful SDK services. Lands the shape only:

  - SdkCallCx — per-call context plumbed into every future service
    trait method (app_id, principal, execution/request ids, trigger
    depth slots).
  - Services — empty non_exhaustive bundle; v1.1.1 (KV) adds the first
    field, subsequent PRs follow.
  - ServiceEventEmitter — async trait future services emit through;
    real outbox-backed impl lands with triggers in v1.1.1. NoopEventEmitter
    is the v1.1.0 default.

No behaviour change. Subsequent commits in this PR plumb these types
through executor-core and the orchestrator dispatch path.

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

crates/shared/src/services.rs

@@ -0,0 +1,38 @@
+//! `Services` — bundle of stateful SDK service handles plumbed from the
+//! host binary into every Rhai execution.
+//!
+//! v1.1.0 ships this struct empty. Subsequent PRs in the v1.1.x series
+//! add one field per service:
+//!
+//! ```ignore
+//! pub kv:   Arc<dyn KvService>,    // v1.1.1
+//! pub docs: Arc<dyn DocsService>,  // v1.1.2
+//! pub http: Arc<dyn HttpService>,  // v1.1.4
+//! // …
+//! ```
+//!
+//! The bundle is cheap to clone (`Arc` per service) and is constructed
+//! once at startup in the picloud binary. The executor takes it by
+//! reference per invocation, hands it (alongside an `SdkCallCx`) to
+//! `executor-core::sdk::register_all`, which wires the corresponding
+//! Rhai `::` namespace per service.
+//!
+//! `#[non_exhaustive]` so adding fields is a non-breaking change for
+//! consumers that only *pattern-match* a `&Services`; only crates that
+//! *construct* a `Services` (in practice, just the picloud binary) need
+//! to update their constructor when new services land.
+
+/// SDK service bundle. See module docs for the lifecycle and the v1.1.x
+/// expansion plan.
+#[non_exhaustive]
+#[derive(Default)]
+pub struct Services {}
+
+impl Services {
+    /// Construct an empty bundle. Replaced by a fielded `::new(...)`
+    /// once the first service (KV, v1.1.1) lands.
+    #[must_use]
+    pub fn new() -> Self {
+        Self {}
+    }
+}