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/ui/components/mod.rs

@@ -1,8 +1,9 @@
-// UI компоненты для переиспользования
+//! Reusable UI components: message bubbles, input fields, modals, lists.
 
 pub mod modal;
 pub mod input_field;
 pub mod message_bubble;
+pub mod message_list;
 pub mod chat_list_item;
 pub mod emoji_picker;
 
@@ -11,3 +12,4 @@ pub use input_field::render_input_field;
 pub use chat_list_item::render_chat_list_item;
 pub use emoji_picker::render_emoji_picker;
 pub use message_bubble::{render_date_separator, render_message_bubble, render_sender_header};
+pub use message_list::{render_message_item, calculate_scroll_offset, render_help_bar};