東北キャラクター追加とデフォルト変更 (#13)

fix: Resolve E2E test failures by updating textarea selectors

refactor: Optimize timeout values for improved test performance

style: Apply comprehensive ruff formatting across entire codebase

feat: Migrate from isort, black, flake8 to ruff for unified linting and formatting

refactor: Update file upload and URL extraction tabs for improved clarity and functionality

refactor: Clean up code formatting and improve readability across multiple files

Refactor unit tests for SessionManager and TextProcessor classes