feat: playback bar component, save system improvements, demo and roadmap updates

engine/core/VideoManager.ts

@@ -155,6 +155,15 @@ export class VideoManager {
     this.active.currentTime = time
   }
 
+  setPlaybackRate(rate: number) {
+    if (this.elA) this.elA.playbackRate = rate
+    if (this.elB) this.elB.playbackRate = rate
+  }
+
+  getPlaybackRate(): number {
+    return this.active?.playbackRate ?? 1
+  }
+
   setMuted(muted: boolean) {
     if (this.elA) this.elA.muted = muted
     if (this.elB) this.elB.muted = muted