refactor: split main_input.rs into modular handlers (1199→164 lines)

Split monolithic input handler into 5 specialized modules:
- handlers/chat.rs (452 lines) - chat keyboard input
- handlers/modal.rs (316 lines) - modal dialogs
- handlers/chat_list.rs (142 lines) - chat list navigation
- handlers/search.rs (140 lines) - search functionality
- handlers/compose.rs (80 lines) - forward/reply/edit modes

Changes:
- main_input.rs: 1199→164 lines (removed 1035 lines, -86%)
- Preserved existing handlers: clipboard, global, profile
- Created clean router pattern in main_input.rs
- Fixed keybinding conflict: Ctrl+I→Ctrl+U for profile
- Fixed modifier handling in chat input (ignore Ctrl/Alt chars)
- Updated CONTEXT.md with refactoring metrics
- Updated ROADMAP.md: Phase 13 Etap 1 marked as DONE

Phase 13 Etap 1: COMPLETED (100%)

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

src/input/handlers/mod.rs

@@ -4,10 +4,20 @@
 //! - global: Global commands (Ctrl+R, Ctrl+S, etc.)
 //! - clipboard: Clipboard operations
 //! - profile: Profile helper functions
+//! - chat: Keyboard input handling for open chat view
+//! - chat_list: Navigation and interaction in the chat list
+//! - compose: Text input, editing, and message composition
+//! - modal: Modal dialogs (delete confirmation, emoji picker, etc.)
+//! - search: Search functionality (chat search, message search)
 
 pub mod clipboard;
 pub mod global;
 pub mod profile;
+pub mod chat;
+pub mod chat_list;
+pub mod compose;
+pub mod modal;
+pub mod search;
 
 pub use clipboard::*;
 pub use global::*;