fix(ui): revert vite base /app/ — broke CSS/JS asset loading

Keep nginx /app/ alias for favicon resolution only.
CSS/JS stay at root-relative paths via location /.

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

vite.config.js

@@ -1,7 +1,6 @@
 import { defineConfig } from 'vite';
 
 export default defineConfig({
-  base: '/app/',
   build: {
     outDir: 'dist',
     assetsDir: 'assets',