1.2.7: 6 more bundled fonts + custom-font upload + layerActiveAt parity

Built-in additions: Montserrat, Nunito, Figtree, Gabarito (sans),
Archivo Black (heavy display), Press Start 2P (pixel/retro).

Custom font upload (lib/fonts.ts):
- uploadCustomFont(file) reads .woff2/.woff/.ttf/.otf via FileReader,
  registers a FontFace early so a corrupt file fails before storage,
  then persists {id, label, dataUrl} to localStorage under
  'animatr:customFonts'. Quota errors surface a friendly message.
- removeCustomFont(id) drops the FontFace + storage entry. If the
  asset still pointed at the deleted font, the picker resets it to
  System Sans on the calling side.
- AVAILABLE_FONTS becomes a ComputedRef combining BUILTIN_FONTS with
  the reactive customFontsState. fontFamilyMapSnapshot() rebuilds the
  {id → CSS family} map per export so user-uploaded fonts make it
  into the exported runtime.

FontPicker UI:
- Two sections divided by a thin rule — built-ins on top, "Your fonts"
  below — plus an "Upload font…" entry at the bottom that opens a
  hidden file input. Custom rows show a trash button on hover.
- Auto-selects a freshly uploaded font.

Engine source becomes a function (engineSource()) instead of a const,
so each export materializes the latest FONT_FAMILY map. ENGINE_TEMPLATE
holds the static skeleton with a __FONT_FAMILY_MAP__ placeholder.

Example HTML hint:
- Built-in fonts list their .woff2 path; custom fonts get a
  "locally uploaded; @font-face below has the file inlined as a data
  URL" line. The fontFaceCss snippet inlines data URLs for custom
  entries so it's self-contained.

Bug fixes (player layerActiveAt):
- Mirrors interpolate.ts isLayerActiveAt now. The previous
  `if(total<=1) return true` short-circuit made layers with a single
  future keyframe visible at t=0; the lastHold→Infinity heuristic
  ignored end keyframes entirely. Both regressions affected the
  fullscreen preview and standalone exports. Replaced with a strict
  scan: min = earliest non-end kf, max = earliest 'end' kf or +Inf.
  Static layers (no normal kfs) stay always-visible.

Tests (5 new under "text font picker — model + render + export"):
- 6 new built-in ids in FONT_FAMILIES map.
- uploadCustomFont registers + persists + appears in AVAILABLE_FONTS;
  removeCustomFont reverses it. Stubs FontFace and document.fonts.add
  for the test environment via a stubFontFaceForTest() helper.
- uploadCustomFont rejects unsupported extensions.
- Exported runtime FONT_FAMILIES includes uploaded custom font ids.
- FontPicker popover shows the Upload font… entry.
- New "exported runtime layerActiveAt mirrors editor isLayerActiveAt"
  extracts the function from engineSource() and exercises five
  scenarios (single future kf, two normal kfs no end, end kf cuts
  off, static layer always-visible, end kf wins over separated tracks).

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

package.json

@@ -1,7 +1,7 @@
 {
   "name": "ruwio",
   "private": true,
-  "version": "1.2.6",
+  "version": "1.2.7",
   "type": "module",
   "scripts": {
     "dev": "vite",