Scope PWA manifest to app's own path instead of origin root

Every installed PWA claimed scope "/", so Android link-capturing routed
navigation for any app on the shared origin into whichever PWA had it.

frontend/vite.config.ts

@@ -15,7 +15,7 @@ export default defineConfig({
         name: 'Calendar',
         short_name: 'Calendar',
         start_url: '/calendar/',
-        scope: '/',
+        scope: '/calendar/',
         display: 'standalone',
         theme_color: '#c9a84c',
         background_color: '#c9a84c',