fix: resolve all 40 clippy warnings (dead_code, unused_imports, lints)

- Add #[allow(unused_imports)] on pub re-exports used only by lib/tests
- Add #[allow(dead_code)] on public API items unused in binary target
- Fix collapsible_if, redundant_closure, unnecessary_map_or in main.rs
- Prefix unused test variables with underscore

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/config/keybindings.rs

@@ -89,10 +89,12 @@ impl KeyBinding {
         Self { key, modifiers: KeyModifiers::CONTROL }
     }
 
+    #[allow(dead_code)]
     pub fn with_shift(key: KeyCode) -> Self {
         Self { key, modifiers: KeyModifiers::SHIFT }
     }
 
+    #[allow(dead_code)]
     pub fn with_alt(key: KeyCode) -> Self {
         Self { key, modifiers: KeyModifiers::ALT }
     }