feat(studio): fullscreen preview mode (F key)

Add distraction-free fullscreen mode using the HTML5 Fullscreen API.
Press F to enter fullscreen (Esc to exit). When active, the composition
fills the screen — timeline, sidebars, and editing overlays are hidden
while all playback shortcuts (Space, J/K/L, arrows, etc.) remain
functional. A fullscreen toggle button is also added to player controls.

Closes #995

packages/studio/src/components/nle/NLELayout.tsx

@@ -1,4 +1,12 @@
-import { useState, useCallback, useRef, useEffect, memo, type ReactNode } from "react";
+import {
+  useState,
+  useCallback,
+  useRef,
+  useEffect,
+  useSyncExternalStore,
+  memo,
+  type ReactNode,
+} from "react";
 import { useMountEffect } from "../../hooks/useMountEffect";
 import { useTimelinePlayer, PlayerControls, Timeline, usePlayerStore } from "../../player";
 import type { TimelineElement } from "../../player";
@@ -71,6 +79,15 @@ const MIN_TIMELINE_H = 100;
 const DEFAULT_TIMELINE_H = 220;
 const MIN_PREVIEW_H = 120;
 
+function subscribeFullscreen(cb: () => void) {
+  document.addEventListener("fullscreenchange", cb);
+  return () => document.removeEventListener("fullscreenchange", cb);
+}
+
+function getFullscreenElement() {
+  return document.fullscreenElement;
+}
+
 export function shouldDisableTimelineWhileCompositionLoading(compositionLoading: boolean): boolean {
   return compositionLoading;
 }
@@ -248,9 +265,20 @@ export const NLELayout = memo(function NLELayout({
     onCompositionLoadingChangeParent?.(compositionLoading);
   }, [compositionLoading, onCompositionLoadingChangeParent]);
 
+  const fullscreenElement = useSyncExternalStore(subscribeFullscreen, getFullscreenElement);
   const isTimelineVisible = timelineVisible ?? true;
   const isDragging = useRef(false);
   const containerRef = useRef<HTMLDivElement>(null);
+  const isFullscreen = fullscreenElement === containerRef.current && fullscreenElement != null;
+
+  const toggleFullscreen = useCallback(() => {
+    if (!containerRef.current) return;
+    if (document.fullscreenElement) {
+      void document.exitFullscreen();
+    } else {
+      void containerRef.current.requestFullscreen();
+    }
+  }, []);
 
   const currentLevel = compositionStack[compositionStack.length - 1];
   const directUrl = compositionStack.length > 1 ? currentLevel.previewUrl : undefined;
@@ -312,6 +340,7 @@ export const NLELayout = memo(function NLELayout({
       className="flex flex-col h-full min-h-0 bg-neutral-950"
       onKeyDown={handleKeyDown}
       tabIndex={-1}
+      data-studio-fullscreen-target=""
     >
       {/* Preview + player controls */}
       <div className="flex-1 min-h-0 flex flex-col">
@@ -326,20 +355,26 @@ export const NLELayout = memo(function NLELayout({
             refreshKey={refreshKey}
             suppressLoadingOverlay={hasLoadedOnceRef.current}
           />
-          {previewOverlay}
+          {!isFullscreen && previewOverlay}
         </div>
         <div className="bg-neutral-950 border-t border-neutral-800/50 flex-shrink-0">
-          {compositionStack.length > 1 && (
+          {!isFullscreen && compositionStack.length > 1 && (
             <CompositionBreadcrumb
               stack={compositionStack}
               onNavigate={handleNavigateComposition}
             />
           )}
-          <PlayerControls onTogglePlay={togglePlay} onSeek={seek} disabled={timelineDisabled} />
+          <PlayerControls
+            onTogglePlay={togglePlay}
+            onSeek={seek}
+            disabled={timelineDisabled}
+            isFullscreen={isFullscreen}
+            onToggleFullscreen={toggleFullscreen}
+          />
         </div>
       </div>
 
-      {isTimelineVisible ? (
+      {!isFullscreen && isTimelineVisible ? (
         <>
           {/* Resize divider */}
           <div
@@ -396,7 +431,7 @@ export const NLELayout = memo(function NLELayout({
             )}
           </div>
         </>
-      ) : onToggleTimeline ? (
+      ) : !isFullscreen && onToggleTimeline ? (
         <div className="flex-shrink-0 border-t border-neutral-800/50 bg-neutral-950/96">
           <div className="flex h-10 items-center justify-between px-3">
             <div className="text-[10px] font-medium uppercase tracking-[0.16em] text-neutral-500">

packages/studio/src/hooks/useAppHotkeys.ts

@@ -248,6 +248,24 @@ export function useAppHotkeys({
       }
     }
 
+    // F — toggle fullscreen preview
+    if (
+      event.key.toLowerCase() === "f" &&
+      !event.metaKey &&
+      !event.ctrlKey &&
+      !event.altKey &&
+      !event.shiftKey &&
+      !isEditableTarget(event.target)
+    ) {
+      event.preventDefault();
+      if (document.fullscreenElement) {
+        void document.exitFullscreen();
+      } else {
+        document.querySelector<HTMLElement>("[data-studio-fullscreen-target]")?.requestFullscreen();
+      }
+      return;
+    }
+
     // Delete / Backspace — remove selected element (timeline clip or preview selection)
     if (
       (event.key === "Delete" || event.key === "Backspace") &&

packages/studio/src/player/components/PlayerControls.tsx

@@ -20,6 +20,7 @@ const SHORTCUT_SECTIONS = [
       { key: "⇧L", label: "Toggle loop" },
       { key: "←/→", label: "Step 1 frame" },
       { key: "⇧←/⇧→", label: "Step 10 frames" },
+      { key: "F", label: "Toggle fullscreen" },
     ],
   },
   {
@@ -49,12 +50,16 @@ interface PlayerControlsProps {
   onTogglePlay: () => void;
   onSeek: (time: number) => void;
   disabled?: boolean;
+  isFullscreen?: boolean;
+  onToggleFullscreen?: () => void;
 }
 
 export const PlayerControls = memo(function PlayerControls({
   onTogglePlay,
   onSeek,
   disabled = false,
+  isFullscreen = false,
+  onToggleFullscreen,
 }: PlayerControlsProps) {
   // Subscribe to only the fields we render — each selector prevents cascading re-renders
   const isPlaying = usePlayerStore((s) => s.isPlaying);
@@ -595,6 +600,60 @@ export const PlayerControls = memo(function PlayerControls({
         </svg>
       </button>
 
+      {/* Fullscreen toggle */}
+      {onToggleFullscreen && (
+        <button
+          type="button"
+          onClick={() => {
+            trackStudioEvent("playback", { action: "fullscreen_toggle", active: !isFullscreen });
+            onToggleFullscreen();
+          }}
+          className={`h-7 w-7 flex-shrink-0 flex items-center justify-center rounded-md border transition-colors ${
+            isFullscreen
+              ? "text-studio-accent bg-studio-accent/10 border-studio-accent/30"
+              : "border-neutral-700 text-neutral-400 hover:border-neutral-500 hover:bg-neutral-800"
+          }`}
+          title={isFullscreen ? "Exit fullscreen (F)" : "Enter fullscreen (F)"}
+          aria-label={isFullscreen ? "Exit fullscreen" : "Enter fullscreen"}
+        >
+          {isFullscreen ? (
+            <svg
+              width="13"
+              height="13"
+              viewBox="0 0 24 24"
+              fill="none"
+              stroke="currentColor"
+              strokeWidth="2"
+              strokeLinecap="round"
+              strokeLinejoin="round"
+              aria-hidden="true"
+            >
+              <path d="M8 3v3a2 2 0 0 1-2 2H3" />
+              <path d="M21 8h-3a2 2 0 0 1-2-2V3" />
+              <path d="M3 16h3a2 2 0 0 1 2 2v3" />
+              <path d="M16 21v-3a2 2 0 0 1 2-2h3" />
+            </svg>
+          ) : (
+            <svg
+              width="13"
+              height="13"
+              viewBox="0 0 24 24"
+              fill="none"
+              stroke="currentColor"
+              strokeWidth="2"
+              strokeLinecap="round"
+              strokeLinejoin="round"
+              aria-hidden="true"
+            >
+              <path d="M8 3H5a2 2 0 0 0-2 2v3" />
+              <path d="M21 8V5a2 2 0 0 0-2-2h-3" />
+              <path d="M3 16v3a2 2 0 0 0 2 2h3" />
+              <path d="M16 21h3a2 2 0 0 0 2-2v-3" />
+            </svg>
+          )}
+        </button>
+      )}
+
       {/* Keyboard shortcuts + frame jump + work area — click to open panel */}
       <div ref={shortcutsPanelRef} className="relative flex-shrink-0">
         <button