refactor: prepare handlers structure for future input refactoring

Preparation for splitting large input file (#2):
- Created src/input/handlers/ structure (7 modules)
  - clipboard.rs (~100 lines) - clipboard operations extracted
  - global.rs (~90 lines) - global commands (Ctrl+R/S/P/F) extracted
  - Stubs: profile.rs, search.rs, modal.rs, messages.rs, chat_list.rs
- main_input.rs remains monolithic (1139 lines)
  - Attempted full migration broke navigation - rolled back
  - Handlers remain as preparation for gradual migration

Updated documentation:
- REFACTORING_OPPORTUNITIES.md: #2.1 status updated
- CONTEXT.md: Added lesson about careful refactoring

Lesson learned: Critical input logic requires careful step-by-step
refactoring with functionality verification after each step.

Tests: 563 passed, 0 failed

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

src/input/handlers/mod.rs

@@ -0,0 +1,26 @@
+//! Input handlers organized by screen/mode
+//!
+//! This module contains handlers for different input contexts:
+//! - global: Global commands (Ctrl+R, Ctrl+S, etc.)
+//! - profile: Profile mode input
+//! - search: Search modes (chat search, message search)
+//! - modal: Modal modes (pinned, reactions, delete, forward)
+//! - messages: Message input when chat is open
+//! - chat_list: Chat list navigation
+//! - clipboard: Clipboard operations
+
+pub mod chat_list;
+pub mod clipboard;
+pub mod global;
+pub mod messages;
+pub mod modal;
+pub mod profile;
+pub mod search;
+
+pub use chat_list::*;
+pub use clipboard::*;
+pub use global::*;
+pub use messages::*;
+pub use modal::*;
+pub use profile::*;
+pub use search::*;