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

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

src/lib/utils/clipRange.ts

@@ -0,0 +1,28 @@
+export type QuickClipPosition = 'at' | 'before';
+
+export function computeQuickClipRange(
+  currentTime: number,
+  duration: number,
+  position: QuickClipPosition,
+  clipDuration = 10,
+): { start: number; end: number } | null {
+  if (duration === 0) return null;
+
+  switch (position) {
+    case 'at':
+      return {
+        start: currentTime,
+        end: Math.min(currentTime + clipDuration, duration),
+      };
+    case 'before':
+      return {
+        start: Math.max(currentTime - clipDuration, 0),
+        end: currentTime,
+      };
+    default: {
+      const _exhaustive: never = position;
+      void _exhaustive;
+      return null;
+    }
+  }
+}