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/package.json

@@ -65,6 +65,7 @@
     "tw-animate-css": "^1.3.4",
     "typescript": "~5.8.3",
     "typescript-eslint": "^8.30.1",
-    "vite": "^6.3.5"
+    "vite": "^6.3.5",
+    "vite-plugin-obfuscator": "^1.0.5"
   }
 }