feat(spf): export ./live-hls + sandbox live-engine harness

Add the ./live-hls subpath export (build entry + package export) and a
LiveHlsEngineSignals type. Add a bare sandbox template (live-hls-engine) that
wires createLiveHlsEngine to a raw <video> — no player/skin — and logs playback
state, for end-to-end live-playback verification.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

packages/spf/src/playback/engines/live-hls/engine.ts

@@ -31,7 +31,12 @@ import { resolvePresentation } from '../../behaviors/resolve-presentation';
 import { setupFailoverMonitor } from '../../behaviors/setup-failover-monitor';
 import { syncPreload } from '../../behaviors/sync-preload';
 import { switchAudioTrack, switchVideoTrack } from '../../behaviors/track-switching';
-import type { SimpleHlsEngineConfig, SimpleHlsEngineContext, SimpleHlsEngineState } from '../hls/engine';
+import type {
+  SimpleHlsEngineConfig,
+  SimpleHlsEngineContext,
+  SimpleHlsEngineSignals,
+  SimpleHlsEngineState,
+} from '../hls/engine';
 
 /** Config for the live HLS engine: the VoD config plus live-only options. */
 export interface LiveHlsEngineConfig extends SimpleHlsEngineConfig {
@@ -44,6 +49,7 @@ export interface LiveHlsEngineConfig extends SimpleHlsEngineConfig {
 
 export type LiveHlsEngineState = SimpleHlsEngineState;
 export type LiveHlsEngineContext = SimpleHlsEngineContext;
+export type LiveHlsEngineSignals = SimpleHlsEngineSignals;
 
 const shareSignals = makeShareSignals<LiveHlsEngineState, LiveHlsEngineContext>([
   'userVideoTrackSelection',

packages/spf/src/playback/engines/live-hls/index.ts

@@ -1,2 +1,7 @@
-export type { LiveHlsEngineConfig, LiveHlsEngineContext, LiveHlsEngineState } from './engine';
+export type {
+  LiveHlsEngineConfig,
+  LiveHlsEngineContext,
+  LiveHlsEngineSignals,
+  LiveHlsEngineState,
+} from './engine';
 export { createLiveHlsEngine } from './engine';