Clean up frontend branding and metadata

Replace Vite defaults with Nuzlocke Tracker branding: custom pokeball-
skull favicon (SVG + PNG + ICO), page title, meta description, Open
Graph tags, theme-color, web manifest, and package.json name.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/public/site.webmanifest

@@ -0,0 +1,11 @@
+{
+  "name": "Nuzlocke Tracker",
+  "short_name": "Nuzlocke",
+  "icons": [
+    { "src": "/icon-192.png", "sizes": "192x192", "type": "image/png" },
+    { "src": "/icon-512.png", "sizes": "512x512", "type": "image/png" }
+  ],
+  "theme_color": "#DC2626",
+  "background_color": "#111827",
+  "display": "standalone"
+}