Add global providers for react-query, theming, and auth

Introduce a new Providers component to manage global contexts including react-query, theme switching, and authentication. Added necessary dependencies: `@tanstack/react-query-devtools` and `next-themes`, and configured default options for react-query.

frontend/package.json

@@ -26,6 +26,7 @@
     "@eslint/eslintrc": "^3",
     "@hey-api/openapi-ts": "^0.64.10",
     "@tailwindcss/postcss": "^4",
+    "@tanstack/react-query-devtools": "^5.67.1",
     "@types/node": "^20.17.23",
     "@types/react": "^19",
     "@types/react-dom": "^19",
@@ -33,6 +34,7 @@
     "eslint-config-next": "15.2.0",
     "eslint-config-prettier": "^10.0.2",
     "eslint-plugin-prettier": "^5.2.3",
+    "next-themes": "^0.4.4",
     "openapi-typescript-codegen": "^0.29.0",
     "prettier": "^3.5.3",
     "tailwindcss": "^4",