feat(sdk): Context::emit for WIT 1.1 host.emit-event (T1)

Brings the module SDK to WIT 1.1 in lockstep with the platform and
exposes the new host.emit-event as an ergonomic ctx.emit(name,
payload). Modules emit ephemeral progress/stream events (progress,
token streaming) delivered live to a following client and never
persisted.

- wit/world.wit → 1.1.0 (host.emit-event + use types.{payload}).
- host.rs: an emit hook (thread-local fn pointer; guest is
  single-threaded). The #[fai_module] expansion installs a closure
  reaching the real WIT emit-event import at the start of each
  invocation; Context::emit calls through it. Outside a hub (unit
  tests) it is a silent no-op.
- examples/progress: reference module emitting progress + token events;
  builds clean for wasm32-wasip2, proving the ergonomics end-to-end.

The SDK keeps shielding module authors: emit is the whole surface, no
wit_bindgen in sight.

Signed-off-by: flemming-it <sf@flemming.it>

crates/chain-module-sdk/src/context.rs

@@ -11,3 +11,23 @@ pub struct Context {
     pub capability_name: String,
     pub deadline_ms: u64,
 }
+
+impl Context {
+    /// Emit an ephemeral progress/stream event during this invocation
+    /// (WIT 1.1 `emit-event`). Delivered live to any client following
+    /// the flow (`SubmitStream`); it is **never** written to the audit
+    /// log. Use it for progress updates or token streaming.
+    ///
+    /// `name` is a caller-defined label (e.g. `"progress"`, `"token"`);
+    /// `payload` is the event body. The host enforces per-invocation
+    /// size + rate limits — an over-limit event is dropped, never an
+    /// error. When the module runs outside a hub that supports it (or
+    /// in a unit test) `emit` is a silent no-op.
+    ///
+    /// ```ignore
+    /// ctx.emit("progress", Payload::Text("50%".into()));
+    /// ```
+    pub fn emit(&self, name: &str, payload: crate::Payload) {
+        crate::emit(name, payload);
+    }
+}