feat(preview): add loop toggle for timeline playback

Adds a loop button next to the play/pause control in the preview
toolbar. When enabled, preview playback wraps back to the start of
the timeline instead of pausing on reaching the end. The state is
persisted as a per-project setting and defaults to off.

- Add optional \`loop: boolean\` field to \`TProjectSettings\`
- Add \`LoopToggleButton\` in the preview toolbar, wired through
  \`UpdateProjectSettingsCommand\` so toggling is undoable
- In \`PlaybackManager.updateTime\`, when the playhead reaches the
  end and the project's \`loop\` setting is on, reset to time zero
  and continue scheduling animation frames instead of pausing.
  The audio manager picks up the seek-to-zero through the existing
  \`onSeek\` listener, so audio restarts in sync with video.

apps/web/src/core/managers/playback-manager.ts

@@ -224,12 +224,26 @@ export class PlaybackManager {
 		const maxTime = this.editor.timeline.getTotalDuration();
 
 		if (newTime >= maxTime) {
+			const shouldLoop =
+				this.editor.project.getActive()?.settings.loop === true &&
+				maxTime > ZERO_MEDIA_TIME;
+
+			if (shouldLoop) {
+				this.playbackStartWallTime = performance.now();
+				this.playbackStartTime = ZERO_MEDIA_TIME;
+				this.currentTime = ZERO_MEDIA_TIME;
+				this.notifySeek(ZERO_MEDIA_TIME);
+				this.dispatchSeekEvent(ZERO_MEDIA_TIME);
+				this.playbackTimer = requestAnimationFrame(this.updateTime);
+				return;
+			}
+
 			this.pause();
 			this.currentTime = maxTime;
 			this.notify();
-		this.notifySeek(maxTime);
-		this.dispatchSeekEvent(maxTime);
-		return;
+			this.notifySeek(maxTime);
+			this.dispatchSeekEvent(maxTime);
+			return;
 		}
 
 		this.currentTime = newTime;

apps/web/src/preview/components/toolbar.tsx

@@ -10,7 +10,10 @@ import {
 	FullScreenIcon,
 	PauseIcon,
 	PlayIcon,
+	RepeatIcon,
+	RepeatOffIcon,
 } from "@hugeicons/core-free-icons";
+import { UpdateProjectSettingsCommand } from "@/commands/project";
 import { HugeiconsIcon } from "@hugeicons/react";
 import { Separator } from "@/components/ui/separator";
 import {
@@ -34,7 +37,10 @@ export function PreviewToolbar({
 	return (
 		<div className="grid grid-cols-[1fr_auto_1fr] items-center pb-3 pt-5 px-5">
 			<TimecodeDisplay />
-			<PlayPauseButton />
+			<div className="justify-self-center flex items-center gap-1">
+				<PlayPauseButton />
+				<LoopToggleButton />
+			</div>
 			<div className="justify-self-end flex items-center gap-2.5">
 				<ZoomSelect />
 				<Separator orientation="vertical" className="h-4" />
@@ -144,3 +150,23 @@ function PlayPauseButton() {
 		</Button>
 	);
 }
+
+function LoopToggleButton() {
+	const loop = useEditor((e) => e.project.getActive()?.settings.loop === true);
+
+	return (
+		<Button
+			type="button"
+			variant={loop ? "secondary" : "text"}
+			size="icon"
+			aria-pressed={loop}
+			aria-label={loop ? "Disable loop playback" : "Enable loop playback"}
+			title={loop ? "Loop is on" : "Loop is off"}
+			onClick={() => {
+				new UpdateProjectSettingsCommand({ loop: !loop }).execute();
+			}}
+		>
+			<HugeiconsIcon icon={loop ? RepeatIcon : RepeatOffIcon} />
+		</Button>
+	);
+}

apps/web/src/project/types.ts

@@ -33,6 +33,11 @@ export interface TProjectSettings {
 	lastCustomCanvasSize?: TCanvasSize | null;
 	originalCanvasSize?: TCanvasSize | null;
 	background: TBackground;
+	/**
+	 * When true, preview playback wraps back to the start of the timeline
+	 * instead of pausing once the playhead reaches the end. Defaults to false.
+	 */
+	loop?: boolean;
 }
 
 export interface TTimelineViewState {