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/types.rs

@@ -1,4 +1,6 @@
-/// Type-safe ID wrappers to prevent mixing up different ID types
+//! Type-safe ID wrappers to prevent mixing up different ID types.
+//!
+//! Provides `ChatId` and `MessageId` newtypes for compile-time safety.
 
 use serde::{Deserialize, Serialize};
 use std::fmt;