fix: use relative base path for Vite assets

When the server-ui is deployed under a subpath (/t/{slug}/), absolute
asset paths (/assets/...) resolve to the domain root instead of the
subpath, causing 404s. Using './' makes asset URLs relative to the
HTML page, so they resolve correctly regardless of mount path.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ui/vite.config.ts

@@ -27,7 +27,7 @@ export default defineConfig({
   optimizeDeps: {
     include: ['swagger-ui-dist/swagger-ui-bundle'],
   },
-  base: '/',
+  base: './',
   build: {
     outDir: 'dist',
   },