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>

tests/helpers/app_builder.rs

@@ -10,6 +10,7 @@ use tele_tui::tdlib::{ChatInfo, MessageInfo};
 use tele_tui::types::{ChatId, MessageId};
 
 /// Builder для создания тестового App с FakeTdClient\n///\n/// Использует trait-based DI для подмены TdClient на FakeTdClient в тестах.
+#[allow(dead_code)]
 pub struct TestAppBuilder {
     config: Config,
     screen: AppScreen,
@@ -34,6 +35,7 @@ impl Default for TestAppBuilder {
     }
 }
 
+#[allow(dead_code)]
 impl TestAppBuilder {
     pub fn new() -> Self {
         Self {