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>

wit/world.wit

@@ -2,7 +2,7 @@
 // FROZEN. Wire contract between hub and modules.
 // =============================================================
 //
-// This file is the stable wire contract between the F∆I Hub
+// This file is the stable wire contract between the Ch∆In Hub
 // and any module compiled against it. It is **frozen at v1.0**.
 //
 // Frozen means:
@@ -20,11 +20,11 @@
 // See `crates/fai_runtime/tests/wit_freeze.rs`.
 //
 // Module authors do NOT depend on this file directly. They
-// use `fai-module-sdk`, which wraps these bindings behind a
+// use `chain-module-sdk`, which wraps these bindings behind a
 // stable, ergonomic surface. That is what protects modules
 // from any future evolution of this contract.
 
-package chain:platform@1.0.0;
+package chain:platform@1.1.0;
 
 /// Types that flow between the host (hub) and modules.
 interface types {
@@ -74,8 +74,19 @@ interface types {
 
 /// The host-provided interface that modules can import to talk back.
 interface host {
+  use types.{payload};
+
   /// Log a structured message. Level is "trace", "debug", "info", "warn", "error".
   log: func(level: string, message: string);
+
+  /// Emit an ephemeral progress/stream event during an invocation.
+  /// Added in 1.1. Events are fanned out to any client following this
+  /// invocation live (SubmitStream); they are NOT written to the
+  /// tamper-evident audit log. `name` is a caller-defined event label
+  /// (e.g. "progress", "token"); `payload` is the event body. The host
+  /// enforces per-invocation size + rate limits — an event over the
+  /// limit is dropped with a warning and never fails the invocation.
+  emit-event: func(name: string, payload: payload);
 }
 
 /// The core interface every module exports.