Refactor view handling and keybinding API

Move the `View` enum to a dedicated module and implement `Widget` for
`&App` there.
Rename `default_view_keybindings` to `default_keybindings` and adjust
its
signature. Redesign `KeybindingsWidget` to accept an explicit list of
bindings instead of a `View`. Update imports, function signatures, and
rendering
logic across the codebase to reflect these changes.

src/cli.rs

@@ -1,4 +1,4 @@
-use crate::app::{GameMode, PerkDecks, View};
+use crate::app::{GameMode, PerkDecks, view::View};
 use clap::Parser;
 
 #[derive(Parser, Debug)]