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/motion.css

@@ -82,6 +82,15 @@
   --nv-travel-sm: 4px;
   --nv-travel-md: 8px;
   --nv-travel-lg: 16px;
+
+  /* --- Sequence ---------------------------------------------------------------
+     The gap between siblings arriving one after another. Short enough that a
+     group reads as one movement, long enough that the eye sees an order. */
+  --nv-stagger: 60ms;
+
+  /* A loading shimmer is a slow, constant sweep — slow enough to read as
+     "waiting", never fast enough to read as an alert. */
+  --nv-duration-shimmer: 1600ms;
 }
 
 /* Reduced motion is a system-wide contract, not a per-component opt-in: cut
@@ -103,5 +112,6 @@
     --nv-travel-sm: 0px;
     --nv-travel-md: 0px;
     --nv-travel-lg: 0px;
+    --nv-stagger: 0ms;
   }
 }