Harden frontend assets: disable source maps, add JS obfuscation, env var config

- Disable source maps in production builds (vite.config.ts: sourcemap: false)
- Add vite-plugin-obfuscator for JS obfuscation (hex identifiers, base64 string encoding)
- Move OIDC config behind VITE_* env vars with dev fallbacks (auth/config.ts)
- Add server_tokens off to nginx.conf to stop advertising nginx version
- Add type declaration for vite-plugin-obfuscator

frontend/nginx.conf

@@ -1,6 +1,7 @@
 server {
     listen 80;
     server_name _;
+    server_tokens off;
 
     # Root directory for static files (must match Docker COPY path)
     root /usr/share/nginx/html;