fix(deploy): serve under /xll-bi/ prefix and bump host port to 8214

Reverse proxy at demo-ctx.lnh2e.com forwards /xll-bi/* unchanged to the
container, so the container's nginx must match that location and Vite
must build asset URLs under the same prefix — otherwise the SPA shell
returns 404 and the JS/CSS resolve to /assets/* with no handler.

- nginx.conf: rename location /bi/ → /xll-bi/ (and assets sub-location)
- vite.config.ts: set base: '/xll-bi/' so built index.html references
  /xll-bi/assets/*
- docker-compose.yml: 8114 → 8214 to match the upstream the proxy targets

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

vite.config.ts

@@ -6,6 +6,7 @@ import {defineConfig, loadEnv} from 'vite';
 export default defineConfig(({mode}) => {
   const env = loadEnv(mode, '.', '');
   return {
+    base: '/xll-bi/',
     plugins: [react(), tailwindcss()],
     define: {
       'process.env.GEMINI_API_KEY': JSON.stringify(env.GEMINI_API_KEY),