0.8.4: button transitions, locked groups revoke edits, UX polish

Button-state transitions
- State flips on stage-preview buttons (normal / hover / pressed /
  disabled) now ease over 50ms instead of snapping. New
  `transitions` map + rAF ticker in useButtonRuntime drive a
  continuous sample time between BUTTON_STATE_TIMES slots;
  CanvasStage samples each button child at that interpolated time
  so keyframes at the 4 states blend smoothly. Mid-flight flips
  (hover → pressed while still in normal → hover) rebase from
  the current live sample instead of snapping.

Locked groups revoke edits
- Locking a layer directly or its enclosing group deselects the
  layer so the Properties panel can't keep editing it. Panel also
  splits into three branches — editable / locked / no-layer —
  with a dedicated locked-layer hint.
- Timeline keyframe interactions (drag, dblclick-to-remove,
  context menu, dblclick-to-create on lane, add-kf toolbar)
  now consult effective lock (direct + parent group) instead
  of just layer.locked.

Editor polish
- Inactive tracks fade as a whole row (opacity 0.5) instead of
  per-child, so keyframes, segments, and still-frame tails stay
  visually proportional to their active counterparts.
- Dragging a layer onto a group's track-name label now drops
  it INTO the group (was previously only the group-lane area).
- Button assets on the stage show a pointer cursor on hover so
  it's obvious they're interactive.
- Global CSS forces `cursor: pointer !important` on every enabled
  button / role="button" so scoped component styles can no longer
  accidentally shadow the default.
- Timeline resize handle jumped above the scrub-bar (z-index 100)
  so the full 14px grab zone is hit-testable again.

Regression tests
- setTrackLocked deselect paths: direct lock, group lock with
  selected child, group lock with unrelated selection, unlock
  doesn't re-select.
- duplicateKeyframeAt: props + easing + hold + bezier copied,
  collision refusal, unknown-id guards, separated-track routing.
- Button transition runtime: no-transition baseline, mid-flight
  bounds, mid-transition rebase, no-op setState.
- Shared composables tooltips + asset-thumbs: same ref across
  calls, localStorage round-trip.

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

src/components/Timeline.vue

@@ -544,14 +544,16 @@ const canCreateKf = computed(() => {
   const id = store.selectedLayerId
   if (!id) return false
   const layer = store.activeLayers.find((l) => l.id === id)
-  return !!layer && !layer.locked
+  if (!layer) return false
+  if (layer.locked) return false
+  return !lockedGroupChildIds.value.has(id)
 })
 
 function addKeyframeForSelected() {
   const id = store.selectedLayerId
   if (!id) return
   const layer = store.activeLayers.find((l) => l.id === id)
-  if (!layer || layer.locked) return
+  if (!layer || isLayerIdLocked(id)) return
   const time = snapTime(store.playhead)
   const sampled = sampleLayer(layer, time)
   const props: Partial<AnimatableProps> = {
@@ -576,7 +578,7 @@ function onLaneDblClick(e: MouseEvent, track: TimelineLayerTrack) {
   const ratio = Math.max(0, Math.min(1, (e.clientX - rect.left) / rect.width))
   const time = snapTime(ratio * duration.value)
   const layer = store.activeLayers.find((l) => l.id === track.layerId)
-  if (!layer || layer.locked) return
+  if (!layer || isLayerIdLocked(track.layerId)) return
   const sampled = sampleLayer(layer, time)
   const props: Partial<AnimatableProps> = {}
   if (track.kind === 'position') {
@@ -617,8 +619,7 @@ function onKeyframeClick(e: MouseEvent, layerId: string, time: number) {
 function onKeyframeDblClick(e: MouseEvent, layerId: string, keyframeId: string) {
   e.stopPropagation()
   if (kfDrag.value?.moved) return
-  const layer = store.activeLayers.find((l) => l.id === layerId)
-  if (layer?.locked) return
+  if (isLayerIdLocked(layerId)) return
   store.removeKeyframe(layerId, keyframeId)
 }
 
@@ -665,6 +666,17 @@ const lockedGroupChildIds = computed(() => {
   return s
 })
 
+/** Effective lock for a bare layer id — direct flag OR reached by a
+ *  locked parent group. Keyframe interactions consult this so edits
+ *  are blocked the moment the containing group is locked, without
+ *  having to look up the TimelineTrack wrapper. */
+function isLayerIdLocked(layerId: string): boolean {
+  const layer = store.activeLayers.find((l) => l.id === layerId)
+  if (!layer) return false
+  if (layer.locked) return true
+  return lockedGroupChildIds.value.has(layerId)
+}
+
 function isTrackEffectivelyLocked(track: TimelineTrack): boolean {
   if (track.type === 'layer') {
     return !!track.layer.locked || lockedGroupChildIds.value.has(track.layerId)
@@ -901,7 +913,7 @@ function onKeyframePointerDown(
 ) {
   if (e.button !== 0) return
   const layer = store.activeLayers.find((l) => l.id === layerId)
-  if (layer?.locked) return
+  if (isLayerIdLocked(layerId)) return
   const kfEl = e.currentTarget as HTMLElement
   const lane = kfEl.parentElement
   if (!lane) return
@@ -1193,6 +1205,7 @@ function onKeyframeContextMenu(
 ) {
   e.preventDefault()
   e.stopPropagation()
+  if (isLayerIdLocked(layerId)) return
   const layer = store.activeLayers.find((l) => l.id === layerId)
   const kf = kfs.find((k) => k.id === keyframeId)
   if (!layer || !kf) return
@@ -2754,12 +2767,16 @@ onBeforeUnmount(() => {
             >
               <span
                 class="track-name group-track-name"
+                :class="{ 'drop-into': dropGroupId === track.groupId }"
                 :draggable="!track.locked"
                 @click="toggleGroupCollapsed(track.groupId)"
                 @dblclick="!track.locked ? renameGroupPrompt(track.groupId, track.name) : null"
                 @contextmenu="!track.locked ? onGroupContextMenu($event, track.groupId) : null"
                 @dragstart="!track.locked ? onTrackDragStart($event, track.groupId) : null"
                 @dragend="onTrackDragEnd"
+                @dragover.stop="!track.locked ? onGroupBodyDragOver($event, track.groupId) : null"
+                @drop.stop="!track.locked ? onGroupBodyDrop($event, track.groupId) : null"
+                @dragleave="onGroupBodyDragLeave"
               >
                 <PhDotsSixVertical :size="12" class="drag-handle" />
                 <component
@@ -3606,13 +3623,19 @@ onBeforeUnmount(() => {
   bottom: -1px;
 }
 
-.track.inactive .track-lane > :not(.playhead) {
-  opacity: 0.4;
+/* Inactive tracks fade as a whole row — same visual vocabulary as
+   the active track, just dimmer. Applying opacity to the row itself
+   keeps keyframes, segments, and the still-frame tail visually in
+   sync (previously we faded each child individually, which multiplied
+   against each child's own opacity and made diamonds read as ghostly
+   while their connecting segments looked nearly normal). */
+.track.inactive {
+  opacity: 0.5;
   transition: opacity 140ms var(--ease);
 }
 
-.track.inactive:hover .track-lane > :not(.playhead) {
-  opacity: 0.75;
+.track.inactive:hover {
+  opacity: 0.85;
 }
 
 .track.locked {