feat: avatar decorations follow-up — Nextcloud CDN, sync script, docs

- Point DECORATION_CDN at Lotus Nextcloud WebDAV share instead of external
  avatardecoration.com; all 99 APNG files are self-hosted and served via
  direct DAV URL (no CORS issue for <img> elements)
- Add onError handler to AvatarDecoration.tsx to silently hide the overlay
  if a file is missing or the CDN is unreachable
- Rewrite scripts/syncDecorations.mjs: now sends HTTP HEAD requests to the
  live Nextcloud CDN (batches of 16 in parallel) and removes catalog entries
  for files that return non-2xx; empty categories are pruned automatically.
  Workflow: delete files from Nextcloud → run `npm run sync:decorations` →
  commit the updated avatarDecorations.ts. No local files needed.
- Add public/decorations/ to .gitignore; delete the 85 MB local APNG cache
  that was downloaded during development (files live on Nextcloud now)
- Add sync:decorations script to package.json
- Update LOTUS_FEATURES.md, LOTUS_TODO.md (P5-13 + P5-14 ✓), README.md
  with avatar decoration documentation and catalog sync workflow

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

LOTUS_TODO.md

@@ -260,7 +260,7 @@ Themes:
 
 ---
 
-### [ ] P5-12 · Seasonal / Event Themes
+### [x] P5-12 · Seasonal / Event Themes
 
 **What:** Automatic + manually toggleable seasonal overlays with CSS particle effects and accent color variants:
 
@@ -274,7 +274,7 @@ Themes:
 
 ---
 
-### [ ] P5-13 · Avatar Frame / Border Decorations
+### [x] P5-13 · Avatar Frame / Border Decorations
 
 **What:** Decorative CSS rings/frames rendered around user avatars. Built-in options: TDS Glow (animated orange pulsing), Cyberpunk (rotating gradient), Minimal (thin ring), Gold (supporter cosmetic). Stored in Matrix account data `io.lotus.avatar_frame`. Only visible in Lotus Chat.  
 **[AUDIT REQUIRED]** Verify folds Avatar component allows overlay decoration without breaking child-type constraints (see previous white-circle avatar bug).  
@@ -282,7 +282,7 @@ Themes:
 
 ---
 
-### [ ] P5-14 · Animated Avatar Overlay Decorations (Discord-style)
+### [x] P5-14 · Animated Avatar Overlay Decorations (Discord-style)
 
 **What:** Animated WebM/GIF overlays that float around avatars (transparent center showing avatar). Curated built-in set OR user-uploaded mxc:// overlay. Stored in account data. Only Lotus Chat users see them.  
 **[AUDIT REQUIRED]** See #P5-13 audit. Also decide: curated set only vs user-uploadable.  
@@ -355,7 +355,7 @@ Themes:
 
 ---
 
-### [ ] P5-34 · User-to-User Private Notes
+### [x] P5-34 · User-to-User Private Notes
 
 **What:** A private "Notes" field on user profiles visible only to you. Syncs across all your devices.  
 **Matrix Tech:** Store in `io.lotus.user_notes` account data. Must be keyed by `userId`.