feat: cut clip from Player mode (X/Z keys, scissors button)

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

src/lib/components/PlayerControls.svelte

@@ -38,12 +38,14 @@
     hasCaptions,
     onToggleCaptions,
     onOpenCaptionSettings,
+    onCutClip,
   }: {
     visible: boolean;
     captionsEnabled: boolean;
     hasCaptions: boolean;
     onToggleCaptions: () => void;
     onOpenCaptionSettings: () => void;
+    onCutClip: (position: 'at' | 'before') => void;
   } = $props();
 
   let showSpeedSelector = $state(false);
@@ -225,6 +227,14 @@
           {/if}
         </div>
 
+        <button
+          class="ctrl-btn"
+          onclick={() => onCutClip('at')}
+          oncontextmenu={(e) => { e.preventDefault(); onCutClip('before'); }}
+          title="Cut clip at playhead (X) · Right-click: 10s before (Z)"
+          type="button"
+        ><Scissors size={16} /></button>
+
         {#if hasCaptions}
           <button
             class="ctrl-btn"