fix: support UTF-8 characters in hotkey matching

- Fix key_matches() to use chars().count() instead of len()
- This correctly handles multi-byte UTF-8 characters (russian layout)
- All 9 config tests now pass (was 7/9, now 9/9)

Fixes:
- test_hotkeys_matches_char_keys
- test_hotkeys_matches_russian_vim_keys

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

src/config.rs

@@ -287,7 +287,8 @@ impl HotkeysConfig {
                     }
                 }
                 // Символьные клавиши (буквы, цифры)
-                key_char if key_char.len() == 1 => {
+                // Проверяем количество символов, а не байтов (для поддержки UTF-8)
+                key_char if key_char.chars().count() == 1 => {
                     if let KeyCode::Char(ch) = key {
                         if let Some(expected_ch) = key_char.chars().next() {
                             if ch == expected_ch {