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/ui/messages.rs

@@ -101,8 +101,6 @@ fn render_input_with_cursor(
 /// Информация о строке после переноса: текст и позиция в оригинале
 struct WrappedLine {
     text: String,
-    /// Начальная позиция в символах от начала оригинального текста
-    start_offset: usize,
 }
 
 /// Разбивает текст на строки с учётом максимальной ширины
@@ -111,14 +109,12 @@ fn wrap_text_with_offsets(text: &str, max_width: usize) -> Vec<WrappedLine> {
     if max_width == 0 {
         return vec![WrappedLine {
             text: text.to_string(),
-            start_offset: 0,
         }];
     }
 
     let mut result = Vec::new();
     let mut current_line = String::new();
     let mut current_width = 0;
-    let mut line_start_offset = 0;
 
     let chars: Vec<char> = text.chars().collect();
     let mut word_start = 0;
@@ -133,7 +129,6 @@ fn wrap_text_with_offsets(text: &str, max_width: usize) -> Vec<WrappedLine> {
                 if current_width == 0 {
                     current_line = word;
                     current_width = word_width;
-                    line_start_offset = word_start;
                 } else if current_width + 1 + word_width <= max_width {
                     current_line.push(' ');
                     current_line.push_str(&word);
@@ -141,11 +136,9 @@ fn wrap_text_with_offsets(text: &str, max_width: usize) -> Vec<WrappedLine> {
                 } else {
                     result.push(WrappedLine {
                         text: current_line,
-                        start_offset: line_start_offset,
                     });
                     current_line = word;
                     current_width = word_width;
-                    line_start_offset = word_start;
                 }
                 in_word = false;
             }
@@ -161,31 +154,26 @@ fn wrap_text_with_offsets(text: &str, max_width: usize) -> Vec<WrappedLine> {
 
         if current_width == 0 {
             current_line = word;
-            line_start_offset = word_start;
         } else if current_width + 1 + word_width <= max_width {
             current_line.push(' ');
             current_line.push_str(&word);
         } else {
             result.push(WrappedLine {
                 text: current_line,
-                start_offset: line_start_offset,
             });
             current_line = word;
-            line_start_offset = word_start;
         }
     }
 
     if !current_line.is_empty() {
         result.push(WrappedLine {
             text: current_line,
-            start_offset: line_start_offset,
         });
     }
 
     if result.is_empty() {
         result.push(WrappedLine {
             text: String::new(),
-            start_offset: 0,
         });
     }