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/keybindings/main_menu.rs

@@ -0,0 +1,14 @@
+use crate::app::{
+    App,
+    keybindings::{Action, event_to_action},
+};
+use ratatui::crossterm::event::KeyEvent;
+
+pub fn main_menu_keybindings(app: &mut App, event: &KeyEvent) {
+    if let Some(action) = event_to_action(&event) {
+        match action {
+            Action::Quit => app.exit = true,
+            _ => (),
+        }
+    }
+}