Migre eslint v8 → v9 (flat config), supprime les dépréciations

- eslint 8 → 9, @typescript-eslint/* → typescript-eslint (package unifié)
- Remplace .eslintrc.json par eslint.config.mjs (backend) et eslint.config.js (frontend)
- Ajoute eslint-plugin-react, eslint-plugin-react-hooks, globals (frontend)
- Supprime rimraf@3, @humanwhocodes/* qui étaient des deps transitives d'eslint v8

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/.eslintrc.json

@@ -1,22 +0,0 @@
-{
-  "env": {
-    "node": true,
-    "es2021": true
-  },
-  "extends": [
-    "eslint:recommended",
-    "plugin:@typescript-eslint/recommended"
-  ],
-  "parser": "@typescript-eslint/parser",
-  "parserOptions": {
-    "ecmaVersion": "latest",
-    "sourceType": "module"
-  },
-  "plugins": [
-    "@typescript-eslint"
-  ],
-  "rules": {
-    "@typescript-eslint/no-unused-vars": "warn",
-    "@typescript-eslint/no-explicit-any": "warn"
-  }
-}

backend/eslint.config.mjs

@@ -0,0 +1,16 @@
+import js from '@eslint/js';
+import tseslint from 'typescript-eslint';
+
+export default tseslint.config(
+  js.configs.recommended,
+  ...tseslint.configs.recommended,
+  {
+    rules: {
+      '@typescript-eslint/no-unused-vars': 'warn',
+      '@typescript-eslint/no-explicit-any': 'warn',
+    },
+  },
+  {
+    ignores: ['dist/**', 'node_modules/**'],
+  }
+);

backend/package.json

@@ -33,9 +33,9 @@
     "@types/bcryptjs": "^2.4.2",
     "typescript": "^5.2.2",
     "tsx": "^4.1.0",
-    "eslint": "^8.50.0",
-    "@typescript-eslint/eslint-plugin": "^6.7.5",
-    "@typescript-eslint/parser": "^6.7.5",
+    "eslint": "^9.18.0",
+    "@eslint/js": "^9.18.0",
+    "typescript-eslint": "^8.22.0",
     "vitest": "^0.34.6"
   }
 }