feat(ui): new equalizer logo, favicon link, fix favicon path

- icon.svg / icon-192/512.png: blue→purple equalizer gradient design
- nginx.conf: add /app/ alias so reverse-proxy prefix resolves assets
- vite.config.js: base /app/ + %BASE_URL% in favicon links so path
  resolves correctly whether app is served at / or /app/
- ic_launcher.xml: same equalizer design for Android app icon

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

index.html

@@ -9,8 +9,8 @@
 <meta name="apple-mobile-web-app-status-bar-style" content="black-translucent">
 <meta name="apple-mobile-web-app-title" content="NovaSonic">
 <link rel="manifest" href="manifest.json">
-<link rel="icon" href="/icon.svg" type="image/svg+xml">
-<link rel="icon" href="/icon-192.png" type="image/png" sizes="192x192">
+<link rel="icon" href="%BASE_URL%icon.svg" type="image/svg+xml">
+<link rel="icon" href="%BASE_URL%icon-192.png" type="image/png" sizes="192x192">
 <link rel="apple-touch-icon" href="icon.svg">
 <title>NovaSonic</title>
 <link rel="preconnect" href="https://fonts.googleapis.com">