Fix ESLint 10 compatibility by migrating to pure flat config

[Copilot]

ESLint 10 removed @eslint/eslintrc and FlatCompat, breaking the existing configuration that relied on these compatibility shims.

Changes

• Removed deprecated compatibility layer: Eliminated FlatCompat and @eslint/eslintrc imports
• Migrated to native flat configs:
  • typescriptEslint.configs['flat/recommended'] instead of compat.extends()
  • jest.configs['flat/recommended'] for Jest plugin
  • Direct import of eslint-config-prettier
• Added globals dependency: Required for defining language globals in flat config

Before/After

// Before: Using deprecated FlatCompat
const compat = new FlatCompat({ baseDirectory: __dirname })
export default [
  ...compat.extends(
    'plugin:@typescript-eslint/recommended',
    'plugin:jest/recommended'
  ),
  // ...
]

// After: Pure flat config
export default [
  ...typescriptEslint.configs['flat/recommended'],
  jest.configs['flat/recommended'],
  prettierConfig,
  // ...
]

Note: Installed with --legacy-peer-deps as TypeScript ESLint v8.55.0 supports ESLint 10 but peer dependency metadata hasn't been updated yet.

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