fix(seasonal): keep Arcade + Deep Space overlays out of the chat text

Arcade:
- perspective grid is masked through the central timeline column so it
  frames the chat instead of striping messages; lower opacity, thinner
  non-scaling strokes (also fixes the grid vanishing in the 76px swatch)
- neon horizon line is broken through the middle so it never underlines
  a message; softer sun glow
- "1UP" score + "INSERT COIN" moved from top-left/bottom-centre (space
  bar / composer) to a single bottom-right HUD stack; font-size clamps
  to 0 via cqw inside the settings swatch so no more clipped glyphs
- scanlines: 4px pitch at lower opacity (light theme was fully striped);
  ambient wash slightly lighter

Deep Space:
- starfield 28 → 62 stars across the two parallax layers
- base violet wash slightly lighter for light themes

SeasonalPreview wrapper is now a size container (container-type) so
overlays can scale/hide fixed-px details with cqw. LOTUS_FEATURES.md
theme table now describes what both overlays actually render.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/app/components/seasonal/SeasonalEffect.tsx

@@ -84,7 +84,15 @@ export function SeasonalPreview({ theme }: { theme: SeasonTheme }) {
   return (
     <div
       aria-hidden="true"
-      style={{ position: 'absolute', inset: 0, overflow: 'hidden', pointerEvents: 'none' }}
+      style={{
+        position: 'absolute',
+        inset: 0,
+        overflow: 'hidden',
+        pointerEvents: 'none',
+        // Size container so overlays can scale/hide fixed-size details (e.g.
+        // Arcade's HUD text) with `cqw` instead of rendering clipped in a swatch.
+        containerType: 'inline-size',
+      }}
     >
       {buildOverlayContent(theme, true)}
     </div>