fix(ci): fix ESLint flat config plugin resolution

- Override react-hooks rules within the same config object that defines the plugin
- Avoids 'Cannot redefine plugin' error in ESLint 9 flat config

web/eslint.config.mjs

@@ -3,7 +3,21 @@ import nextVitals from "eslint-config-next/core-web-vitals";
 import nextTs from "eslint-config-next/typescript";
 
 const eslintConfig = defineConfig([
-  ...nextVitals,
+  ...nextVitals.map((cfg) => {
+    // Downgrade React 19 strict rules to warnings (fix incrementally)
+    if (cfg?.rules?.["react-hooks/rules-of-hooks"]) {
+      return {
+        ...cfg,
+        rules: {
+          ...cfg.rules,
+          "react-hooks/rules-of-hooks": "warn",
+          "react-hooks/set-state-in-effect": "off",
+          "react-hooks/purity": "warn",
+        },
+      };
+    }
+    return cfg;
+  }),
   ...nextTs,
   // Override default ignores of eslint-config-next.
   globalIgnores([
@@ -15,10 +29,6 @@ const eslintConfig = defineConfig([
   ]),
   {
     rules: {
-      // Downgrade React 19 strict rules to warnings (fix incrementally)
-      "react-hooks/rules-of-hooks": "warn",
-      "react-hooks/set-state-in-effect": "off",
-      "react-hooks/purity": "warn",
       "@typescript-eslint/no-this-alias": "warn",
       "@typescript-eslint/no-require-imports": "warn",
     },