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/lib/interpolate.ts

@@ -134,6 +134,12 @@ function sampleKeyframeSet(
  *
  * Returns null (→ always visible) when the layer has zero or one total
  * keyframes — a single keyframe is a static layer with no animation range.
+ *
+ * Special case: when the keyframe with the latest time has `hold: true`,
+ * the max is extended to Infinity — the layer stays alive past its last
+ * keyframe, pinned to that keyframe's sampled value. That's how users
+ * turn the final keyframe of a short anim into a still frame so the
+ * layer stays on-screen for the remainder of the timeline.
  */
 export function layerActiveRange(
   layer: Layer,
@@ -145,12 +151,19 @@ export function layerActiveRange(
   if (total <= 1) return null
   let min = Infinity
   let max = -Infinity
+  let lastHold = false
   for (const arr of [main, pos, rot]) {
     for (const k of arr) {
       if (k.time < min) min = k.time
-      if (k.time > max) max = k.time
+      if (k.time > max) {
+        max = k.time
+        lastHold = !!k.hold
+      } else if (k.time === max && k.hold) {
+        lastHold = true
+      }
     }
   }
+  if (lastHold) max = Infinity
   return { min, max }
 }