refactor: add modal/validation utils and partial App encapsulation

Quick wins refactoring (Variant 1):
- Created src/utils/modal_handler.rs (120+ lines)
  - 4 functions for modal handling (close, confirm, yes/no)
  - ModalAction enum for type-safe processing
  - English and Russian keyboard layout support
  - 4 unit tests
- Created src/utils/validation.rs (180+ lines)
  - 7 validation functions (empty, length, IDs, etc)
  - Covers all common validation patterns
  - 7 unit tests
- Partial App encapsulation:
  - Made config field private (readonly via app.config())
  - Added 30+ getter/setter methods
  - Updated ui/messages.rs to use config()
- Updated documentation:
  - REFACTORING_OPPORTUNITIES.md: #1 Complete, #5 Partial
  - CONTEXT.md: Added quick wins section

Tests: 563 passed, 0 failed

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

src/utils/modal_handler.rs

@@ -0,0 +1,184 @@
+//! Modal dialog utilities
+//!
+//! Переиспользуемая логика для обработки модальных окон (диалогов).
+
+use crossterm::event::KeyCode;
+
+/// Результат обработки клавиши в модальном окне.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum ModalAction {
+    /// Закрыть модалку (Escape была нажата)
+    Close,
+    /// Подтвердить действие (Enter была нажата)
+    Confirm,
+    /// Продолжить обработку ввода (другая клавиша)
+    Continue,
+}
+
+/// Обрабатывает стандартные клавиши для модальных окон.
+///
+/// Проверяет клавиши Escape (закрыть) и Enter (подтвердить).
+/// Если нажата другая клавиша, возвращает `Continue`.
+///
+/// # Arguments
+///
+/// * `key_code` - код нажатой клавиши
+///
+/// # Returns
+///
+/// * `ModalAction::Close` - если нажата Escape
+/// * `ModalAction::Confirm` - если нажата Enter
+/// * `ModalAction::Continue` - для других клавиш
+///
+/// # Examples
+///
+/// ```
+/// use crossterm::event::KeyCode;
+/// use tele_tui::utils::modal_handler::{handle_modal_key, ModalAction};
+///
+/// assert_eq!(handle_modal_key(KeyCode::Esc), ModalAction::Close);
+/// assert_eq!(handle_modal_key(KeyCode::Enter), ModalAction::Confirm);
+/// assert_eq!(handle_modal_key(KeyCode::Char('a')), ModalAction::Continue);
+/// ```
+pub fn handle_modal_key(key_code: KeyCode) -> ModalAction {
+    match key_code {
+        KeyCode::Esc => ModalAction::Close,
+        KeyCode::Enter => ModalAction::Confirm,
+        _ => ModalAction::Continue,
+    }
+}
+
+/// Проверяет, нужно ли закрыть модалку (нажата Escape).
+///
+/// # Examples
+///
+/// ```
+/// use crossterm::event::KeyCode;
+/// use tele_tui::utils::modal_handler::should_close_modal;
+///
+/// assert!(should_close_modal(KeyCode::Esc));
+/// assert!(!should_close_modal(KeyCode::Enter));
+/// assert!(!should_close_modal(KeyCode::Char('q')));
+/// ```
+pub fn should_close_modal(key_code: KeyCode) -> bool {
+    matches!(key_code, KeyCode::Esc)
+}
+
+/// Проверяет, нужно ли подтвердить действие в модалке (нажата Enter).
+///
+/// # Examples
+///
+/// ```
+/// use crossterm::event::KeyCode;
+/// use tele_tui::utils::modal_handler::should_confirm_modal;
+///
+/// assert!(should_confirm_modal(KeyCode::Enter));
+/// assert!(!should_confirm_modal(KeyCode::Esc));
+/// assert!(!should_confirm_modal(KeyCode::Char('y')));
+/// ```
+pub fn should_confirm_modal(key_code: KeyCode) -> bool {
+    matches!(key_code, KeyCode::Enter)
+}
+
+/// Обрабатывает клавиши для подтверждения Yes/No.
+///
+/// Поддерживает:
+/// - `y` / `Y` / `д` / `Д` - да (confirm)
+/// - `n` / `N` / `т` / `Т` - нет (close)
+/// - `Enter` - подтвердить (confirm)
+/// - `Esc` - отменить (close)
+///
+/// # Arguments
+///
+/// * `key_code` - код нажатой клавиши
+///
+/// # Returns
+///
+/// * `Some(true)` - подтверждение (yes/Enter)
+/// * `Some(false)` - отмена (no/Escape)
+/// * `None` - другая клавиша (продолжить ввод)
+///
+/// # Examples
+///
+/// ```
+/// use crossterm::event::KeyCode;
+/// use tele_tui::utils::modal_handler::handle_yes_no;
+///
+/// assert_eq!(handle_yes_no(KeyCode::Char('y')), Some(true));
+/// assert_eq!(handle_yes_no(KeyCode::Char('Y')), Some(true));
+/// assert_eq!(handle_yes_no(KeyCode::Char('д')), Some(true)); // русская 'y'
+/// assert_eq!(handle_yes_no(KeyCode::Enter), Some(true));
+///
+/// assert_eq!(handle_yes_no(KeyCode::Char('n')), Some(false));
+/// assert_eq!(handle_yes_no(KeyCode::Char('т')), Some(false)); // русская 'n'
+/// assert_eq!(handle_yes_no(KeyCode::Esc), Some(false));
+///
+/// assert_eq!(handle_yes_no(KeyCode::Char('a')), None);
+/// ```
+pub fn handle_yes_no(key_code: KeyCode) -> Option<bool> {
+    match key_code {
+        // Yes - подтверждение (английская и русская раскладка)
+        KeyCode::Char('y') | KeyCode::Char('Y') | KeyCode::Char('д') | KeyCode::Char('Д') => {
+            Some(true)
+        }
+        KeyCode::Enter => Some(true),
+
+        // No - отмена (английская и русская раскладка)
+        KeyCode::Char('n') | KeyCode::Char('N') | KeyCode::Char('т') | KeyCode::Char('Т') => {
+            Some(false)
+        }
+        KeyCode::Esc => Some(false),
+
+        // Другие клавиши - продолжить
+        _ => None,
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_handle_modal_key() {
+        assert_eq!(handle_modal_key(KeyCode::Esc), ModalAction::Close);
+        assert_eq!(handle_modal_key(KeyCode::Enter), ModalAction::Confirm);
+        assert_eq!(handle_modal_key(KeyCode::Char('a')), ModalAction::Continue);
+        assert_eq!(handle_modal_key(KeyCode::Up), ModalAction::Continue);
+    }
+
+    #[test]
+    fn test_should_close_modal() {
+        assert!(should_close_modal(KeyCode::Esc));
+        assert!(!should_close_modal(KeyCode::Enter));
+        assert!(!should_close_modal(KeyCode::Char('q')));
+    }
+
+    #[test]
+    fn test_should_confirm_modal() {
+        assert!(should_confirm_modal(KeyCode::Enter));
+        assert!(!should_confirm_modal(KeyCode::Esc));
+        assert!(!should_confirm_modal(KeyCode::Char('y')));
+    }
+
+    #[test]
+    fn test_handle_yes_no() {
+        // Yes variants
+        assert_eq!(handle_yes_no(KeyCode::Char('y')), Some(true));
+        assert_eq!(handle_yes_no(KeyCode::Char('Y')), Some(true));
+        assert_eq!(handle_yes_no(KeyCode::Char('д')), Some(true)); // Russian
+        assert_eq!(handle_yes_no(KeyCode::Char('Д')), Some(true)); // Russian
+        assert_eq!(handle_yes_no(KeyCode::Enter), Some(true));
+
+        // No variants
+        assert_eq!(handle_yes_no(KeyCode::Char('n')), Some(false));
+        assert_eq!(handle_yes_no(KeyCode::Char('N')), Some(false));
+        assert_eq!(handle_yes_no(KeyCode::Char('т')), Some(false)); // Russian
+        assert_eq!(handle_yes_no(KeyCode::Char('Т')), Some(false)); // Russian
+        assert_eq!(handle_yes_no(KeyCode::Esc), Some(false));
+
+        // Other keys
+        assert_eq!(handle_yes_no(KeyCode::Char('a')), None);
+        assert_eq!(handle_yes_no(KeyCode::Up), None);
+        assert_eq!(handle_yes_no(KeyCode::Char(' ')), None);
+    }
+}