feat(branding): auto-generate icons on vite build/dev start

vite-branding.ts now exports brandAssetsPlugin() — a Vite plugin
whose buildStart hook runs scripts/generate-pwa-assets.mjs once per
build / dev-server start. All 9 vite configs register it first in
plugins[], so PWA icons under public/icons/ are guaranteed to exist
before VitePWA's includeAssets / manifest.icons get processed and
before the public/ → dist/ copy.

Removes the "did you remember to pnpm generate-pwa-assets?" failure
mode. Dev mode now also auto-populates icons (no more dev 404s on
/icons/favicon.ico).

Verified build from clean state (no public/icons/ pre-existing): the
plugin generates, all 6 icons land in dist-wallet/icons/.

Part of aiolabs/webapp#95.

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

vite.config.ts

@@ -5,7 +5,7 @@ import { defineConfig } from 'vite'
 import Inspect from 'vite-plugin-inspect'
 import { ViteImageOptimizer } from 'vite-plugin-image-optimizer'
 import { visualizer } from 'rollup-plugin-visualizer'
-import { brand, brandAlias } from './vite-branding'
+import { brand, brandAlias, brandAssetsPlugin } from './vite-branding'
 
 // https://vite.dev/config/
 //
@@ -26,6 +26,7 @@ export default defineConfig(({ mode }) => ({
     strictPort: true,
   },
   plugins: [
+    brandAssetsPlugin(),
     vue(),
     tailwindcss(),
     Inspect(),