fix: QA round 2 — playhead guard, controls position, caption lift, Tauri fullscreen, timeline sync

- Guard drawPlayhead on session.duration > 0 in PlayerTimeline
- Move floating controls pill from bottom: 24px to 48px
- Add playerControlsVisible prop to VideoPlayer; captions slide up 160px when controls visible
- Replace web Fullscreen API with Tauri getCurrentWindow().setFullscreen() (WKWebView compat)
- Add core:window:allow-set-fullscreen and core:window:allow-is-fullscreen permissions
- Tie PlayerTimeline visibility to showPlayerControls; remove unused proximity logic

Co-authored-by: Cursor <cursoragent@cursor.com>

src/lib/components/PlayerControls.svelte

@@ -115,11 +115,9 @@
     }, 100);
   }
 
-  function handleFullscreen() {
-    toggleFullscreen();
-    setTimeout(() => {
-      fullscreenActive = isFullscreenActive();
-    }, 100);
+  async function handleFullscreen() {
+    await toggleFullscreen();
+    fullscreenActive = await isFullscreenActive();
   }
 
   function handleCCContextMenu(e: MouseEvent) {
@@ -129,9 +127,9 @@
 
   // Sync PiP/fullscreen/rate state periodically
   $effect(() => {
-    const interval = setInterval(() => {
+    const interval = setInterval(async () => {
       pipActive = isPiPActive();
-      fullscreenActive = isFullscreenActive();
+      fullscreenActive = await isFullscreenActive();
       currentRate = getPlaybackRate();
     }, 500);
     return () => clearInterval(interval);
@@ -279,7 +277,7 @@
 <style>
   .player-controls-overlay {
     position: absolute;
-    bottom: 24px;
+    bottom: 48px;
     left: 15%;
     right: 15%;
     pointer-events: none;

src/lib/components/PlayerTimeline.svelte

@@ -56,7 +56,9 @@
     }
 
     // Draw playhead
-    drawPlayhead(ctx, timelineState, session.currentTime);
+    if (session.duration > 0) {
+      drawPlayhead(ctx, timelineState, session.currentTime);
+    }
 
     ctx.restore();
   }

src/lib/components/VideoPlayer.svelte

@@ -20,8 +20,10 @@
 
   let {
     captionsEnabled = $bindable(true),
+    playerControlsVisible = false,
   }: {
     captionsEnabled?: boolean;
+    playerControlsVisible?: boolean;
   } = $props();
 
   let videoElement = $state<HTMLVideoElement | null>(null);
@@ -232,7 +234,7 @@
       <track kind="captions" />
     </video>
     {#if activeCues.length > 0}
-      <div class="caption-overlay" style={captionPosition}>
+      <div class="caption-overlay" class:lifted={isPlayerMode && playerControlsVisible} style={captionPosition}>
         {#each activeCues as cue}
           <span
             class="caption-text"
@@ -325,6 +327,11 @@
     pointer-events: none;
     z-index: 5;
     padding: 0 10%;
+    transition: transform 0.2s ease;
+  }
+
+  .caption-overlay.lifted {
+    transform: translateY(-160px);
   }
 
   .caption-text {