Add user settings page and PWA install support

- Add profile update, password change, and account deletion endpoints
- Create Settings page with profile editing, password change, and danger zone
- Add Settings link to user dropdown menu in Layout
- Add /settings route to App.tsx
- Add API functions for profile management
- Create PWA manifest.json and add meta tags to index.html

frontend/public/manifest.json

@@ -0,0 +1,12 @@
+{
+  "name": "Vynl - AI Music Discovery",
+  "short_name": "Vynl",
+  "description": "Discover music you'll love with AI",
+  "start_url": "/dashboard",
+  "display": "standalone",
+  "background_color": "#FFF7ED",
+  "theme_color": "#7C3AED",
+  "icons": [
+    { "src": "/favicon.svg", "sizes": "any", "type": "image/svg+xml" }
+  ]
+}