Add depth and light: glow, tiles, avatars, stats, steps, decks, skeletons, reveal

Tokens
- --nv-color-glow role (light and dark) and a glow scale: --nv-glow-sm/md/lg,
  --nv-glow-blur-*, --nv-glow-spread-*, --nv-glow-strength
- --nv-stagger (0ms under reduced motion) and --nv-duration-shimmer

Components
- Card: --lit (lit top edge in --nv-card-tint), --glow, --spotlight
  (light follows the pointer); light layers combine with every elevation
- Tile: small raised key for a glyph or product mark; --solid, --glow, sizes
- Avatar: raised disc with --ring / --glow, sizes, __status, avatar group
- Stat: readings set into one recessed well (.nv-stat-group)
- Steps: markers set into a rail; done steps light their stretch; vertical
- Deck: one surface in front of stacked layers of its kind
- Skeleton: recessed placeholder with a slow sweep, still under reduced motion
- Text: .nv-text-lit and .nv-text-lit--accent

Continuity
- .nv-reveal / .nv-reveal-group: content arrives once as it scrolls into view
  (nv-arrive keyframe); niveus.js marks pending state, so nothing is hidden
  without the script or under reduced motion
- niveus.js tracks the pointer for .nv-card--spotlight

README and REFERENCE document every new class, token and attribute;
tools/check.py passes and dist/ is rebuilt.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

niveus/tokens/elevation.css

@@ -95,4 +95,30 @@
   --nv-focus-ring:
     0 0 0 1px var(--nv-color-focus-ring-contrast),
     0 0 0 calc(1px + var(--nv-focus-ring-width)) var(--nv-color-focus-ring);
+
+  /* --- Glow ------------------------------------------------------------------
+     Light a surface emits rather than the shade it casts. Glow is for things
+     that are *on* — a live status, the selected item in a showcase, a lit key —
+     and it always sits beside an elevation, never instead of one: a glowing
+     surface still rests on something.
+
+     The geometry is a scale like elevation. The color is the component's: a
+     tinted surface glows in its own tint, mixed down to --nv-glow-strength. */
+  --nv-glow-strength: 40%;
+  --nv-glow-blur-sm: 12px;
+  --nv-glow-spread-sm: -2px;
+  --nv-glow-blur-md: 28px;
+  --nv-glow-spread-md: -6px;
+  --nv-glow-blur-lg: 64px;
+  --nv-glow-spread-lg: -12px;
+}
+
+/* The accent glows are declared on every branded subtree as well as the root:
+   a var() inside a custom property resolves where the property is declared, so
+   a root-only declaration would glow in the root brand everywhere. */
+:root,
+[data-nv-brand] {
+  --nv-glow-sm: 0 0 var(--nv-glow-blur-sm) var(--nv-glow-spread-sm) var(--nv-color-glow);
+  --nv-glow-md: 0 0 var(--nv-glow-blur-md) var(--nv-glow-spread-md) var(--nv-color-glow);
+  --nv-glow-lg: 0 0 var(--nv-glow-blur-lg) var(--nv-glow-spread-lg) var(--nv-color-glow);
 }