refactor: cleanup unused code and warnings

Comprehensive cleanup of unused methods, dead code, and compiler warnings:

## Removed Methods (15):
- Duplicate delegation methods: is_authenticated, get_typing_text, get_user_name from TdClient
- Obsolete methods: TdClient::init() (duplicated in main.rs)
- Unused getters: UserCache::{get_username, get_name, get_user_id_by_chat}
- Unused builder methods: MessageBuilder::{edited, add_reaction}
- Unused utility: ChatState::is_normal()
- Dead code: HotkeysConfig::{matches, key_matches} (kept for tests)
- Unused method: UserCache::register_private_chat()
- Getter replaced with direct field access: MessageInfo::edit_date()

## Removed Module:
- error.rs - Unused error handling module (TeletuiError, ErrorVariant, IntoTeletuiError)

## Removed Constants (8):
- EMOJI_PICKER_COLUMNS, EMOJI_PICKER_ROWS, MAX_INPUT_HEIGHT
- MIN_TERMINAL_WIDTH, MIN_TERMINAL_HEIGHT
- TDLIB_CHAT_LIMIT, MAX_USERNAME_DISPLAY_LENGTH, MESSAGE_TEXT_INDENT

## Fixed Warnings:
- Removed unused imports (8 instances)
- Fixed unreachable patterns (10 instances)
- Fixed irrefutable if let patterns (2 instances)
- Fixed unused variables (1 instance)
- Removed dead_code annotations where appropriate

## Improvements:
- Integrated Config::load_credentials() into TdClient::new() for better credential management
- Replaced edit_date() getter with direct field access (message.metadata.edit_date)
- Updated tests to use direct field access instead of removed getters

## Test Results:
All tests passing: 499 passed, 0 failed

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

src/constants.rs

@@ -16,25 +16,6 @@ pub const MAX_CHATS: usize = 200;
 /// Максимальное количество user_ids для хранения в чате
 pub const MAX_CHAT_USER_IDS: usize = 500;
 
-// ============================================================================
-// UI Constants
-// ============================================================================
-
-/// Количество колонок в emoji picker сетке
-pub const EMOJI_PICKER_COLUMNS: usize = 8;
-
-/// Количество рядов в emoji picker сетке
-pub const EMOJI_PICKER_ROWS: usize = 6;
-
-/// Максимальная высота поля ввода (в строках)
-pub const MAX_INPUT_HEIGHT: usize = 10;
-
-/// Минимальная ширина терминала для корректного отображения
-pub const MIN_TERMINAL_WIDTH: u16 = 80;
-
-/// Минимальная высота терминала для корректного отображения
-pub const MIN_TERMINAL_HEIGHT: u16 = 20;
-
 // ============================================================================
 // Performance
 // ============================================================================
@@ -52,18 +33,5 @@ pub const LAZY_LOAD_USERS_PER_TICK: usize = 5;
 // TDLib
 // ============================================================================
 
-/// Лимит количества чатов для загрузки через TDLib за раз
-pub const TDLIB_CHAT_LIMIT: i32 = 50;
-
 /// Лимит количества сообщений для загрузки через TDLib за раз
 pub const TDLIB_MESSAGE_LIMIT: i32 = 50;
-
-// ============================================================================
-// Formatting
-// ============================================================================
-
-/// Максимальная длина имени пользователя для отображения
-pub const MAX_USERNAME_DISPLAY_LENGTH: usize = 20;
-
-/// Отступ для wrap текста сообщений
-pub const MESSAGE_TEXT_INDENT: usize = 2;