feat(branding): new app logo for Tauri + PWA install

Replaced Tauri icon source (icon.png) with new 1024px wheat-stalk
mark on dark background. Regenerated all platform variants via
`tauri icon`: macOS .icns, Windows .ico, Linux PNGs, iOS AppIcon
set, Android adaptive icon foregrounds.

Web: PWA manifest icons (192/512) and apple-touch-icon now use the
new logo. Browser-tab favicon (favicon.svg) unchanged — keeps the
theme-aware wheat mark.

Tauri app: 0.5.1 → 0.5.2.

static/manifest.json

@@ -8,17 +8,17 @@
   "theme_color": "#5E81AC",
   "background_color": "#2E3440",
   "icons": [
-    {
-      "src": "/favicon.svg",
-      "sizes": "any",
-      "type": "image/svg+xml",
-      "purpose": "any"
-    },
     {
       "src": "/favicon-192.png",
       "sizes": "192x192",
       "type": "image/png",
       "purpose": "any maskable"
+    },
+    {
+      "src": "/favicon-512.png",
+      "sizes": "512x512",
+      "type": "image/png",
+      "purpose": "any maskable"
     }
   ]
 }