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/lib.rs

@@ -7,23 +7,29 @@
 pub mod app;
 pub mod auth;
 pub mod error;
+pub mod events;
 pub mod execution_log;
 pub mod ids;
 pub mod log_sink;
 pub mod route;
 pub mod sandbox;
 pub mod script;
+pub mod sdk_cx;
+pub mod services;
 pub mod validator;
 pub mod version;
 
 pub use app::{App, AppDomain, DomainShape};
 pub use auth::{AppRole, InstanceRole, Principal, Scope, UserId};
 pub use error::Error;
+pub use events::{EmitError, NoopEventEmitter, ServiceEvent, ServiceEventEmitter};
 pub use execution_log::{ExecutionLog, ExecutionStatus};
 pub use ids::{AdminUserId, ApiKeyId, AppId, ExecutionId, RequestId, ScriptId};
 pub use log_sink::{ExecutionLogSink, LogSinkError};
 pub use route::{HostKind, PathKind, Route};
 pub use sandbox::ScriptSandbox;
 pub use script::Script;
+pub use sdk_cx::SdkCallCx;
+pub use services::Services;
 pub use validator::{ScriptValidator, ValidationError};
 pub use version::{API_VERSION, PRODUCT_VERSION, SDK_VERSION, WIRE_VERSION};