style: marker now uses pointer cursor, bold-not-underline on select, red by default

- cursor: pointer signals the click-to-jump affordance more clearly
  than ew-resize (which suggested "drag only")
- selected marker switches to font-weight 700 on the label instead of
  underlining it
- default --marker-color is now a classic red (#ef4444). User can
  still override per-marker via setMarkerColor.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/components/Timeline.vue

@@ -2889,9 +2889,9 @@ onBeforeUnmount(() => {
      when the playhead has snapped onto the marker's position. */
   z-index: 21;
   pointer-events: auto;
-  cursor: ew-resize;
+  cursor: pointer;
   touch-action: none;
-  --marker-color: var(--accent);
+  --marker-color: #ef4444;
 }
 
 .timeline-marker::before {
@@ -2936,7 +2936,7 @@ onBeforeUnmount(() => {
 }
 
 .timeline-marker.selected .timeline-marker-label {
-  text-decoration: underline;
+  font-weight: 700;
 }
 
 .scrub-handle {