chore(deps): update dependency postcss to v8.5.9

Author: renovate[bot]

package.json

@@ -49,7 +49,7 @@
     "@types/node": "24.3.3",
     "@types/react": "19.1.12",
     "eslint": "9.35.0",
-    "postcss": "8.5.6",
+    "postcss": "8.5.9",
     "prettier": "3.6.2",
     "prettier-plugin-tailwindcss": "0.6.14",
     "tailwindcss": "4.1.13",