feat(pwa): make dashboard installable as a progressive web app

Add web manifest, service worker with cache-first static assets and
network-first navigation, and register from the App component head.

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

assets/manifest.json

@@ -0,0 +1,17 @@
+{
+  "name": "CERTifAI Dashboard",
+  "short_name": "CERTifAI",
+  "description": "Self-hosted GenAI infrastructure management dashboard",
+  "start_url": "/dashboard",
+  "display": "standalone",
+  "background_color": "#0f1117",
+  "theme_color": "#4B3FE0",
+  "icons": [
+    {
+      "src": "/assets/logo.svg",
+      "sizes": "any",
+      "type": "image/svg+xml",
+      "purpose": "any maskable"
+    }
+  ]
+}