feat: support CMD as prefix for keybindings in macOS

[erickgnavar]

No description provided.

[roramirez]

I appreciate the contribution! A few things needed before this can merge:

Tests - please add test cases covering:

• Cmd+T → Action::NewTab (happy path)
• Cmd+<unmapped key> → Action::None (guard fires)
• Ctrl+Cmd+T → Action::NewTab (both modifiers held)
• Cmd+<key> in InputMode::Insert vs InputMode::Normal

CHANGELOG - add an entry under ## [Unreleased]:

Added

• support Cmd key as Ctrl equivalaent for keybindings on macOS

[roramirez]

Suggested change

	if cmd && !ctrl && matches!(action, Action::SendToPty(_)) {
	// macOS: Consume any Cmd+key that has no binding, even when Ctrl is also held.
	// Without this, Cmd+Ctrl+<unmapped> would leak a control byte to the PTY.
	if cmd && matches!(action, Action::SendToPty(_)) {

These two modifiers are orthogonal — CTRL and SUPER should be independent bits with no exclusion logic between them. The !ctrl guard should be dropped.

Also, I would change the comment mentioned before