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-branding.ts

@@ -1,5 +1,7 @@
+import { spawnSync } from 'node:child_process'
 import { readFileSync } from 'node:fs'
 import { resolve } from 'node:path'
+import type { Plugin } from 'vite'
 
 /**
  * Absolute path to the active brand kit. Deployers point this at their
@@ -51,3 +53,28 @@ export const brandAlias = {
 export function brandManifestName(appLabel?: string): string {
   return appLabel ? `${brand.name} ${appLabel}` : brand.name
 }
+
+/**
+ * Vite plugin: regenerate PWA icons under public/icons/ once per build
+ * / dev-server start, so vite.<app>.config.ts's includeAssets +
+ * manifest.icons always have something to include. Source resolution
+ * lives in pwa-assets.config.ts.
+ */
+export function brandAssetsPlugin(): Plugin {
+  let generated = false
+  return {
+    name: 'brand-assets-generator',
+    buildStart() {
+      if (generated) return
+      const { status } = spawnSync(
+        'node',
+        [resolve('scripts/generate-pwa-assets.mjs')],
+        { stdio: 'inherit' },
+      )
+      if (status !== 0) {
+        throw new Error('pwa-assets-generator failed; see output above')
+      }
+      generated = true
+    },
+  }
+}