fix: unstretched PWA icons, maskable purpose, theme-aware favicon

- generate-icons.py: preserve SVG aspect ratio (was stretched 1.49x), art at 80% for maskable safe zone, emit transparent cross-gold.png
- manifest icons: purpose 'any maskable'
- applyTheme(): compose favicon per app theme (chrome bg + gold cross)

vite.config.ts

@@ -51,8 +51,8 @@ export default defineConfig({
         theme_color: '#1a1a2e',
         orientation: 'portrait',
         icons: [
-          { src: '/icons/icon-192.png', sizes: '192x192', type: 'image/png' },
-          { src: '/icons/icon-512.png', sizes: '512x512', type: 'image/png' },
+          { src: '/icons/icon-192.png', sizes: '192x192', type: 'image/png', purpose: 'any maskable' },
+          { src: '/icons/icon-512.png', sizes: '512x512', type: 'image/png', purpose: 'any maskable' },
         ],
       },
     }),