0.8.0: group colour cascade, still-frame past end, project rename, UX polish

Headline:

- Group colour cascades to every non-overridden child (layer or clip
  track). New `colorOverridden` flag on Layer / ClipTrack / ScriptTrack
  / TrackGroup; setTrackColor on a non-group pins the track, clearing
  re-inherits from the parent group. moveTrackIntoGroup also inherits.
  normalizeScene migrates legacy scenes (existing colour ⇒ overridden).
- Keyframes inside a button-asset timeline snap to the 4 state slots
  (normal/hover/pressed/disabled). upsertKeyframe / setKeyframeTime /
  duplicateKeyframe all enforce it; colliding drags refuse the move,
  duplicates walk to the nearest free slot.
- Backspace / Delete on a selected layer removes it (respecting the
  layer's own lock and any enclosing group lock).
- "Still frame" allowed on the last keyframe: the layer stays on stage
  past its final kf. Timeline draws a solid dim tail line from the
  last kf to the end, and single-keyframe tracks now show a full-span
  line so on-stage/off-stage reads at a glance. Height stays 3px.
- Project name moved next to the logo, turns into a rename button on
  hover (pencil fades in). Rename syncs the stored record when the
  project is already persisted.
- Shadow + blur keyframes animate in the preview and exported runtime:
  the runtime's lerpProps used to drop them, so every preview rendered
  shadow=0 between keyframes. RUNTIME_VERSION 11 → 13 (covers the
  button-mask + shadow fixes). Held-last-kf also taught to the runtime.
- Button masks render across every path: edit-mode mask-preview,
  nested buttons on the main stage, sidebar thumbnails, fullscreen
  preview + exports. drawButtonFrame new in render.ts.

Smaller fixes:

- Dragging layer A on the stage with a stale selection on layer B used
  to move B and snap A back. Now the shift-selected branch only runs
  when the dragged layer is itself in the selection.
- Clip-track row was missing its icon — PhFilmStrip was referenced but
  never imported. Added, plus dropped the bespoke `gap` on clip / script
  name rows so their icon+label spacing matches layer rows.
- Clip-art drawer pre-lays-out its 400px grid behind `overflow: hidden`
  so slide-in reveals a finished grid instead of reflowing auto-fill
  columns over 220ms.
- Timeline clip-track dropzone hides until the library has a clip; its
  "drop a clip here" hint stays centred in the visible ruler area.
- Keyframe context menu: check-mark and icons share a single 12px column
  so the ✓ on an easing option lines up with PhPauseCircle / PhCopy /
  PhTrash on the rows below. "Still frame"'s active indicator moved to
  the trailing-check slot.
- Button editor's mask-preview now shows the button's own stage instead
  of leaking through to the main scene. drawButtonFrame drives it.

Regression tests cover all of the above: group-color cascade, pin,
clear-re-inherit, migration, button-kf snap and collision rules,
backspace-deletes-selected-layer (incl. lock guards + editable-target
guard), still-frame-past-end visibility, clipart drawer rigid width,
mask rendering in drawButtonFrame / drawSceneFrame, shadow + blur
interpolation in both canvas and runtime paths.

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

src/components/Timeline.vue

@@ -8,6 +8,7 @@ import {
   PhCode,
   PhCopy,
   PhDotsSixVertical,
+  PhFilmStrip,
   PhFolder,
   PhFolderPlus,
   PhLock,
@@ -1062,12 +1063,35 @@ interface KfSegment {
   toTime: number
   easing: Easing
   held: boolean
+  /** True when this segment is the "still-frame tail" extending past
+   *  the last keyframe to the end of the timeline. Rendered dimmer so
+   *  it reads as an after-image rather than an interpolation. */
+  tail?: boolean
 }
 
-function segmentsOf(kfs: Keyframe[]): KfSegment[] {
-  if (kfs.length < 2) return []
+function segmentsOf(kfs: Keyframe[], duration: number): KfSegment[] {
+  if (kfs.length === 0) return []
   const sorted = [...kfs].sort((a, b) => a.time - b.time)
   const out: KfSegment[] = []
+
+  // Single keyframe means the layer is always visible (no animation
+  // range), so the line should span the entire timeline as a solid
+  // dim "on-stage" indicator — same treatment as a still-frame tail.
+  if (sorted.length === 1) {
+    const only = sorted[0]
+    if (duration > 0) {
+      out.push({
+        id: `${only.id}>full`,
+        fromTime: 0,
+        toTime: duration,
+        easing: only.easing,
+        held: false,
+        tail: true,
+      })
+    }
+    return out
+  }
+
   for (let i = 0; i < sorted.length - 1; i++) {
     const a = sorted[i]
     const b = sorted[i + 1]
@@ -1079,6 +1103,20 @@ function segmentsOf(kfs: Keyframe[]): KfSegment[] {
       held: !!a.hold,
     })
   }
+  // Last-keyframe "still frame" tail: when the final keyframe is held,
+  // extend the on-stage indicator to the end of the timeline. Solid
+  // and dim — the value isn't interpolating, it's just idling.
+  const last = sorted[sorted.length - 1]
+  if (last.hold && duration > last.time) {
+    out.push({
+      id: `${last.id}>tail`,
+      fromTime: last.time,
+      toTime: duration,
+      easing: last.easing,
+      held: false,
+      tail: true,
+    })
+  }
   return out
 }
 
@@ -1974,6 +2012,20 @@ function onDocumentKeyDown(e: KeyboardEvent) {
       store.removeMarker(id)
       return
     }
+    // Selected-track deletion. Only layer tracks carry a selection
+    // today (clip / script / group tracks don't set selectedLayerId).
+    // Skip the delete when the layer is locked directly or through its
+    // parent group — Backspace should respect the same locks that block
+    // mouse interaction.
+    if (store.selectedLayerId) {
+      const layerId = store.selectedLayerId
+      const layer = store.activeLayers.find((l) => l.id === layerId)
+      if (!layer) return
+      if (layer.locked || lockedGroupChildIds.value.has(layerId)) return
+      e.preventDefault()
+      store.removeLayer(layerId)
+      return
+    }
   }
   if (
     e.key.toLowerCase() === 'm' &&
@@ -2390,10 +2442,10 @@ onBeforeUnmount(() => {
               >
                 <span class="playhead" :style="{ left: pxFromTime(store.playhead) + 'px' }" />
                 <span
-                  v-for="seg in segmentsOf(track.kfs)"
+                  v-for="seg in segmentsOf(track.kfs, duration)"
                   :key="seg.id"
                   class="kf-seg"
-                  :class="[seg.held ? 'held' : `easing-${seg.easing}`]"
+                  :class="[seg.held ? 'held' : `easing-${seg.easing}`, { tail: seg.tail }]"
                   :style="segmentStyle(seg)"
                 />
                 <span
@@ -2777,14 +2829,13 @@ onBeforeUnmount(() => {
           :disabled="menu.isFirst || menu.isHeld"
           @click="applyEasing(opt.value)"
         >
-          <span class="check">
+          <span class="kf-menu-icon">
             <PhCheck
               v-if="menu.currentEasing === opt.value && !menu.isHeld"
               :size="12"
               weight="bold"
             />
           </span>
-          <span class="kf-menu-icon-spacer"></span>
           {{ opt.label }}
         </button>
         <div v-if="menu.isFirst" class="kf-menu-note">{{ t('timeline.firstKfHint') }}</div>
@@ -2794,24 +2845,23 @@ onBeforeUnmount(() => {
       <button
         class="kf-menu-item"
         :class="{ active: menu.isHeld }"
-        :disabled="menu.isLast"
-        :title="menu.isLast ? t('timeline.lastKfHint') : ''"
         @click="toggleHold"
       >
-        <span class="check">
-          <PhCheck v-if="menu.isHeld" :size="12" weight="bold" />
-        </span>
         <PhPauseCircle :size="12" class="kf-menu-icon" />
         {{ t('timeline.stillFrame') }}
+        <PhCheck
+          v-if="menu.isHeld"
+          :size="12"
+          weight="bold"
+          class="kf-menu-trailing-check"
+        />
       </button>
       <div class="kf-menu-divider"></div>
       <button class="kf-menu-item" @click="duplicateFromMenu">
-        <span class="check"></span>
         <PhCopy :size="12" class="kf-menu-icon" />
         {{ t('timeline.duplicate') }}
       </button>
       <button class="kf-menu-item danger" @click="deleteFromMenu">
-        <span class="check"></span>
         <PhTrash :size="12" class="kf-menu-icon" />
         {{ t('timeline.delete') }}
       </button>
@@ -3803,6 +3853,21 @@ onBeforeUnmount(() => {
   opacity: 0.7;
 }
 
+/* "Tail" = on-stage indicator where the layer is visible but no
+   interpolation is happening (still-frame past the last keyframe, or
+   a single-keyframe layer that's always on stage). Solid line at low
+   opacity — reads as "layer idling on stage" rather than "thin line".
+   Overrides any preceding easing-* gradient background so the fill is
+   always a flat accent colour at the track's tint. */
+.kf-seg.tail,
+.kf-seg.tail.easing-linear,
+.kf-seg.tail.easing-easeIn,
+.kf-seg.tail.easing-easeOut,
+.kf-seg.tail.easing-easeInOut {
+  background: var(--track-color, var(--accent));
+  opacity: 0.35;
+}
+
 .kf {
   position: absolute;
   top: 50%;
@@ -3871,10 +3936,6 @@ onBeforeUnmount(() => {
   color: var(--text-dim);
 }
 
-.clip-track-name {
-  gap: 6px;
-}
-
 .clip-lane {
   position: relative;
 }
@@ -3896,10 +3957,6 @@ onBeforeUnmount(() => {
   color: var(--text-dim);
 }
 
-.script-track-name {
-  gap: 6px;
-}
-
 .script-lane {
   position: relative;
 }
@@ -4238,18 +4295,7 @@ onBeforeUnmount(() => {
   background: var(--danger-soft);
 }
 
-.check {
-  width: 14px;
-  height: 12px;
-  display: inline-flex;
-  align-items: center;
-  justify-content: center;
-  color: var(--accent);
-  flex-shrink: 0;
-}
-
-.kf-menu-icon,
-.kf-menu-icon-spacer {
+.kf-menu-icon {
   width: 12px;
   height: 12px;
   flex-shrink: 0;