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/app/methods/search.rs

@@ -51,9 +51,11 @@ pub trait SearchMethods<T: TdClientTrait> {
     fn update_search_query(&mut self, new_query: String);
 
     /// Get index of selected search result
+    #[allow(dead_code)]
     fn get_search_selected_index(&self) -> Option<usize>;
 
     /// Get all search results
+    #[allow(dead_code)]
     fn get_search_results(&self) -> Option<&[MessageInfo]>;
 }