fix: post-smoke-test polish — preserve playhead, clip list redesign, play-clip action, 1100x750 default

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

src/lib/components/TimelineContextMenu.svelte

@@ -6,6 +6,7 @@
     | { type: 'mark-out' }
     | { type: 'go-to-clip-start' }
     | { type: 'go-to-clip-end' }
+    | { type: 'play-clip' }
     | { type: 'delete-clip' };
 
   let {
@@ -126,6 +127,14 @@
 
   {#if selectedClipId}
     <div class="separator"></div>
+    <button
+      class="menu-item"
+      role="menuitem"
+      onclick={() => handleAction({ type: 'play-clip' })}
+    >
+      <span class="label">Play Clip</span>
+      <span class="shortcut">▶</span>
+    </button>
     <button
       class="menu-item danger"
       role="menuitem"