feat(branding): drive PWA manifest from brand.json

vite-branding.ts now loads brand.json into a typed `brand` object and
exports a `brandManifestName()` helper. Schema:

  { name (required), shortName?, themeColor?, backgroundColor? }

Default brand.json drops themeColor/backgroundColor — they're optional
overrides; per-app accents (wallet yellow, chat green, …) keep working
via `?? '<existing>'` fallbacks in each standalone's vite config.

events: manifest.name/short_name driven by brand. VITE_APP_NAME env
override stays (Phase 2 server-deploy migration still in flight) and,
when set, overrides both name and short_name to preserve pre-#95
behavior. cfaun's VITE_APP_NAME=Bouge keeps working unchanged.

hub (vite.config.ts): brand.name flows into %VITE_APP_NAME% Hub title.

7 other standalones (wallet, chat, market, forum, tasks, restaurant,
libra): only theme_color/background_color get brand overrides. Their
manifest.name/short_name stay hardcoded so multi-PWA home-screen
labels remain differentiated ("Wallet", "Chat", …) rather than all
collapsing to the brand short_name.

Verified default build: events manifest name=AIO; wallet keeps
"Wallet — Lightning" + #eab308 accent.
Verified VITE_APP_NAME=Sortir override: events name+short_name=Sortir.

Part of aiolabs/webapp#95.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

branding/default/brand.json

@@ -1,6 +1,4 @@
 {
   "name": "AIO",
-  "shortName": "AIO",
-  "themeColor": "#ffffff",
-  "backgroundColor": "#ffffff"
+  "shortName": "AIO"
 }