Introduce a centralized shortcut system with ShortcutAction enum and bindings table in shortcuts.rs. Global shortcuts are processed at the top of XserialApp::ui() before any widget rendering. Text input focus is detected via wants_keyboard_input() to suppress shortcuts when typing. Also fix pre-existing import ordering in panels/config.rs from cargo fmt.
Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)
Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>
