docs: update LOTUS_TODO + README for P5-4 and glassmorphism fix

Mark P5-4 (animated chat backgrounds) complete with implementation
notes. Update README Settings section with animated backgrounds entry
and correct glassmorphism description (now explains the body-background
fix that makes backdrop-filter actually visible).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

LOTUS_TODO.md

@@ -978,7 +978,7 @@ Themes:
 
 ---
 
-### [ ] P5-4 · Animated Chat Backgrounds (CSS-animated wallpapers)
+### [x] P5-4 · Animated Chat Backgrounds (CSS-animated wallpapers)
 
 **What:** 5 new animated wallpaper options in the chat background picker:
 
@@ -991,6 +991,8 @@ Themes:
    **[AUDIT REQUIRED]** Study how existing wallpapers are applied in `lotus-terminal.css.ts` to extend the system correctly.  
    **Complexity:** Medium.
 
+**COMPLETED June 2026.** Five new CSS-only animated backgrounds added to the chat background picker via vanilla-extract keyframes: **Digital Rain** (two-layer vertical stripe scroll with parallax depth — wide stripes at 8s, narrow at 4s), **Star Drift** (three-layer radial-gradient dots drifting diagonally), **Grid Pulse** (orange/cyan neon grid lines expanding/contracting via backgroundSize keyframe), **Aurora Flow** (four large radial gradient ellipses sweeping across a 200% canvas), **Fireflies** (three layers of warm glowing radial-gradient dots drifting). All implemented in `src/app/styles/Animations.css.ts` (keyframes) + `src/app/features/lotus/chatBackground.ts` (CSSProperties). `getChatBg` updated with optional `pauseAnimations?: boolean` parameter; also respects `prefers-reduced-motion: reduce` by checking `window.matchMedia` at call time. "Pause Background Animations" toggle added to Settings → Appearance. Glassmorphism sidebar bug fixed simultaneously: sidebar now applies chat background to `document.body` so `backdrop-filter` has content to blur through (previously sidebar was a flex sibling with nothing behind it).
+
 ---
 
 ### [x] P5-5 · Night Light / Blue Light Filter