refactor: complete Phase 13 deep architecture refactoring (etaps 3-7)

Split monolithic files into modular architecture:
- ui/messages.rs (893→365 lines): extract modals/, compose_bar.rs
- tdlib/messages.rs (836→3 files): split into messages/mod, convert, operations
- config/mod.rs (642→3 files): extract validation.rs, loader.rs
- Code duplication cleanup: shared components, ~220 lines removed
- Documentation: PROJECT_STRUCTURE.md rewrite, 16 files got //! docs

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/input/main_input.rs

@@ -1,32 +1,32 @@
+//! Main screen input router.
+//!
+//! Dispatches keyboard events to specialized handlers based on current app mode.
+//! Priority order: modals → search → compose → chat → chat list.
+
 use crate::app::App;
+use crate::app::methods::{
+    compose::ComposeMethods,
+    messages::MessageMethods,
+    modal::ModalMethods,
+    navigation::NavigationMethods,
+    search::SearchMethods,
+};
 use crate::tdlib::TdClientTrait;
 use crate::input::handlers::{
-    copy_to_clipboard, format_message_for_clipboard, get_available_actions_count,
     handle_global_commands,
     modal::{
         handle_profile_mode, handle_profile_open, handle_delete_confirmation,
         handle_reaction_picker_mode, handle_pinned_mode,
     },
-    search::{
-        handle_chat_search_mode, handle_message_search_mode, perform_message_search,
-    },
-    compose::{
-        handle_forward_mode, forward_selected_message,
-    },
-    chat_list::{
-        handle_chat_list_navigation, select_folder, open_chat_and_load_data,
-    },
+    search::{handle_chat_search_mode, handle_message_search_mode},
+    compose::handle_forward_mode,
+    chat_list::handle_chat_list_navigation,
     chat::{
-        handle_message_selection, handle_enter_key, send_reaction,
-        load_older_messages_if_needed, handle_open_chat_keyboard_input,
+        handle_message_selection, handle_enter_key,
+        handle_open_chat_keyboard_input,
     },
 };
-use crate::tdlib::ChatAction;
-use crate::types::{ChatId, MessageId};
-use crate::utils::{is_non_empty, with_timeout, with_timeout_msg, with_timeout_ignore};
-use crate::utils::modal_handler::handle_yes_no;
-use crossterm::event::{KeyCode, KeyEvent};
-use std::time::{Duration, Instant};
+use crossterm::event::KeyEvent;