Update Vite configuration to use base path from environment and simplify proxy settings; adjust main entry point for BrowserRouter basename.

frontend/vite.config.js

@@ -2,32 +2,22 @@ import { defineConfig, loadEnv } from 'vite'
 import react from '@vitejs/plugin-react'
 import tailwindcss from '@tailwindcss/vite'
 
-// https://vite.dev/config/
 export default defineConfig(({ mode }) => {
   const env = loadEnv(mode, import.meta.dirname, '')
   const proxyTarget = env.VITE_API_PROXY_TARGET || 'http://localhost:8000'
+  const base = env.VITE_BASE_PATH || '/'
 
   return {
+    base,
     plugins: [react(), tailwindcss()],
     server: {
       host: true,
-      // Needed for HTTPS tunnels like ngrok during OAuth callback flows.
-      // We allow all hosts in dev to avoid host-blocking when ngrok URL rotates.
       allowedHosts: true,
       port: 5173,
       proxy: {
-        // El backend agrupa todo bajo /api (researchers, export, …).
-        // Con un único prefijo evitamos tener que mantener una entrada
-        // por router cada vez que se añada un endpoint nuevo.
-        '/api': {
-          target: proxyTarget,
-          changeOrigin: true,
-        },
-        '/health': {
-          target: proxyTarget,
-          changeOrigin: true,
-        },
+        '/api': { target: proxyTarget, changeOrigin: true },
+        '/health': { target: proxyTarget, changeOrigin: true },
       },
     },
   }
-})
+})