Refactor keybinding handling and update widgets

- Remove the old `keybindings.rs` and stop re‑exporting its symbols.
- Add view‑specific handling: `App::handle_key_event` now delegates to
  `main_menu_keybindings` when the view is `MainMenu`.
- Update imports in `app.rs`, `widget.rs`, and widget modules to use the
  new `app::keybindings` path.
- Enhance `keybindings_widget` to display ↑, ↓ and “Space” for special
  keys.
- Change main menu layout percentages from 90/10 to 87/13.
- Reorder the `clap` import in `cli.rs` for consistency.

src/app/mod.rs

@@ -4,6 +4,3 @@ pub mod widget;
 pub mod widgets;
 
 pub use app::{App, Event, View, handle_input_events};
-pub use keybindings::{
-    Action, KEYBINDINGS, KeyBinding, binding_for, binding_for_view, event_to_action,
-};