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/config/keybindings.rs

@@ -230,8 +230,8 @@ impl Keybindings {
 
         // Profile
         bindings.insert(Command::OpenProfile, vec![
-            KeyBinding::with_ctrl(KeyCode::Char('i')),
-            KeyBinding::with_ctrl(KeyCode::Char('ш')), // RU
+            KeyBinding::with_ctrl(KeyCode::Char('u')),  // Ctrl+U instead of Ctrl+I
+            KeyBinding::with_ctrl(KeyCode::Char('г')), // RU
         ]);
 
         Self { bindings }