fix: paste not working in PTY sessions (#89)

* fix: Enable paste operations in PTY mode sessions

Resolves clipboard paste issues in PTY SSH sessions by implementing
bracketed paste mode support and handling Event::Paste events.

Changes:
- Enable bracketed paste mode in TerminalStateGuard::new()
- Disable bracketed paste mode in restore_terminal_state()
- Add Event::Paste handler in handle_input_event()
- Increase SmallVec capacity from 8 to 64 bytes for paste content
- Update PtyMessage::LocalInput to use SmallVec<[u8; 64]>
- Add comprehensive unit tests for paste event handling

This fixes paste operations on all platforms (macOS Cmd+V, Linux
Ctrl+Shift+V, Windows Ctrl+V) by properly capturing and forwarding
pasted content through the SSH channel.

Tests: All 455 tests pass, including 8 new paste event tests

* fix: Add paste size limit and optimize memory handling

- Add 1MB size limit to prevent memory exhaustion attacks (H1 issue)
- Return None for empty paste to avoid unnecessary channel sends (M1 issue)
- Use from_vec() instead of into_bytes() + from_slice() to avoid double copy (L1 issue)
- Add test for paste size limit behavior

* style: Apply cargo fmt formatting to test assertions

* test: Add comprehensive tests for key input handling

- Add tests for all Ctrl+key combinations (C, D, Z, A, E, U, K, W, L, R, B, F)
- Add tests for arrow keys (Up, Down, Left, Right)
- Add tests for all function keys (F1-F12) and verify F13+ returns None
- Add tests for special keys (Enter, Tab, Backspace, Esc, Home, End, PageUp, PageDown, Insert, Delete)
- Add tests for KeyEventKind::Release and Repeat being ignored
- Add tests for modifier keys (Shift accepted, Alt/Meta ignored for chars)
- Add tests for Unicode and emoji character input
- Add test for mouse events returning None
- Add test for Ctrl+char out of range

Author: inureyes

src/pty/mod.rs

@@ -91,8 +91,8 @@ pub enum PtyState {
 #[derive(Debug)]
 pub enum PtyMessage {
     /// Data from local terminal to send to remote
-    /// SmallVec<[u8; 8]> keeps key sequences stack-allocated
-    LocalInput(SmallVec<[u8; 8]>),
+    /// SmallVec<[u8; 64]> handles both key sequences and paste content without allocation
+    LocalInput(SmallVec<[u8; 64]>),
     /// Data from remote to display on local terminal
     /// SmallVec<[u8; 64]> handles most terminal output without allocation
     RemoteOutput(SmallVec<[u8; 64]>),