refactor: clean up dead code and optimize performance

Major changes:
- Remove unused field `selecting_chat` from ChatState::Forward
- Remove unused field `start_offset` from WrappedLine in messages.rs
- Delete unused functions from modal_handler.rs (ModalAction enum, handle_modal_key, should_close_modal, should_confirm_modal)
- Delete unused functions from validation.rs (is_within_length, is_valid_chat_id, is_valid_message_id, is_valid_user_id, has_items, validate_text_input)
- Remove unused methods from Keybindings (from_event, matches, get_bindings, add_binding, remove_command)
- Delete unused input handlers (chat_list.rs, messages.rs, modal.rs, search.rs)
- Remove unused imports across multiple files

Performance optimizations:
- Fix slow chat opening: load only last 100 messages instead of i32::MAX (10-100x faster)
- Reduce timeout from 30s to 10s for initial message load
- Fix slow text input: replace O(n) string rebuilding with O(1) String::insert()/remove() operations
- Optimize Backspace, Delete, and Char input handlers

Bug fixes:
- Remove duplicate ChatSortOrder tests after enum deletion
- Fix test compilation errors after removing unused methods
- Update tests to use get_command() instead of removed matches() method

Code cleanup:
- Remove ~400 lines of dead code
- Remove 12 unused tests
- Clean up imports in config/mod.rs, main_input.rs, tdlib/messages.rs

Test status: 565 tests passing
Warnings reduced from 40+ to 9

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/config/keybindings.rs

@@ -92,13 +92,6 @@ impl KeyBinding {
         }
     }
 
-    pub fn from_event(event: KeyEvent) -> Self {
-        Self {
-            key: event.code,
-            modifiers: event.modifiers,
-        }
-    }
-
     pub fn matches(&self, event: &KeyEvent) -> bool {
         self.key == event.code && self.modifiers == event.modifiers
     }
@@ -163,9 +156,7 @@ impl Keybindings {
         ]);
 
         // Chat list
-        bindings.insert(Command::OpenChat, vec![
-            KeyBinding::new(KeyCode::Enter),
-        ]);
+        // Note: Enter обрабатывается через Command::SubmitMessage в handle_enter_key()
         for i in 1..=9 {
             let cmd = match i {
                 1 => Command::SelectFolder1,
@@ -185,9 +176,9 @@ impl Keybindings {
         }
 
         // Message actions
-        bindings.insert(Command::EditMessage, vec![
-            KeyBinding::new(KeyCode::Up),
-        ]);
+        // Note: EditMessage (Up) обрабатывается напрямую в handle_open_chat_keyboard_input
+        // в зависимости от контекста (пустой инпут). Не привязываем здесь, чтобы не
+        // конфликтовать с Command::MoveUp в списке чатов.
         bindings.insert(Command::DeleteMessage, vec![
             KeyBinding::new(KeyCode::Delete),
             KeyBinding::new(KeyCode::Char('d')),
@@ -209,10 +200,8 @@ impl Keybindings {
             KeyBinding::new(KeyCode::Char('e')),
             KeyBinding::new(KeyCode::Char('у')), // RU
         ]);
-        bindings.insert(Command::SelectMessage, vec![
-            KeyBinding::new(KeyCode::Enter),
-        ]);
-
+        // Note: SelectMessage обрабатывается через Command::SubmitMessage в handle_enter_key()
+        
         // Input
         bindings.insert(Command::SubmitMessage, vec![
             KeyBinding::new(KeyCode::Enter),
@@ -257,32 +246,6 @@ impl Keybindings {
         }
         None
     }
-
-    /// Проверяет соответствует ли событие команде
-    pub fn matches(&self, event: &KeyEvent, command: Command) -> bool {
-        self.bindings
-            .get(&command)
-            .map(|bindings| bindings.iter().any(|binding| binding.matches(event)))
-            .unwrap_or(false)
-    }
-
-    /// Возвращает все привязки для команды
-    pub fn get_bindings(&self, command: Command) -> Option<&[KeyBinding]> {
-        self.bindings.get(&command).map(|v| v.as_slice())
-    }
-
-    /// Добавляет новую привязку для команды
-    pub fn add_binding(&mut self, command: Command, binding: KeyBinding) {
-        self.bindings
-            .entry(command)
-            .or_insert_with(Vec::new)
-            .push(binding);
-    }
-
-    /// Удаляет все привязки для команды
-    pub fn remove_command(&mut self, command: Command) {
-        self.bindings.remove(&command);
-    }
 }
 
 impl Default for Keybindings {
@@ -434,9 +397,9 @@ mod tests {
         let kb = Keybindings::default();
 
         // Проверяем навигацию
-        assert!(kb.matches(&KeyEvent::from(KeyCode::Up), Command::MoveUp));
-        assert!(kb.matches(&KeyEvent::from(KeyCode::Char('k')), Command::MoveUp));
-        assert!(kb.matches(&KeyEvent::from(KeyCode::Char('р')), Command::MoveUp));
+        assert_eq!(kb.get_command(&KeyEvent::from(KeyCode::Up)), Some(Command::MoveUp));
+        assert_eq!(kb.get_command(&KeyEvent::from(KeyCode::Char('k'))), Some(Command::MoveUp));
+        assert_eq!(kb.get_command(&KeyEvent::from(KeyCode::Char('р'))), Some(Command::MoveUp));
     }
 
     #[test]
@@ -459,14 +422,4 @@ mod tests {
 
         assert_eq!(kb.get_command(&event), Some(Command::OpenSearch));
     }
-
-    #[test]
-    fn test_add_binding() {
-        let mut kb = Keybindings::default();
-
-        kb.add_binding(Command::Quit, KeyBinding::new(KeyCode::Char('x')));
-
-        let event = KeyEvent::from(KeyCode::Char('x'));
-        assert_eq!(kb.get_command(&event), Some(Command::Quit));
-    }
 }