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/cli.rs

@@ -1,6 +1,5 @@
-use clap::Parser;
-
 use crate::app::View;
+use clap::Parser;
 
 #[derive(Parser, Debug)]
 #[command(version, about = "War in Tunnels", long_about = "War in Tunnels")]