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/app/methods/compose.rs

@@ -3,6 +3,7 @@
 //! Handles reply, forward, and draft functionality
 
 use crate::app::{App, ChatState};
+use crate::app::methods::messages::MessageMethods;
 use crate::tdlib::{MessageInfo, TdClientTrait};
 
 /// Compose methods for reply/forward/draft