macos: special case handling of some control keys

Some control key combinations must be handled specially by Ghostty to
prevent undesirable behavior at the OS level. For now, this includes
only Ctrl-/, which makes a "beep" sound when processed by AppKit. It is
unclear why this beep occurs and no answer was found after extensive
searching.

This solution is inspired by iTerm2, which also handles certain control
key combinations (including C-/) manually before passing them on to
Cocoa/AppKit.

macos/Sources/Ghostty/SurfaceView.swift

@@ -783,7 +783,7 @@ extension Ghostty {
             
             let action = event.isARepeat ? GHOSTTY_ACTION_REPEAT : GHOSTTY_ACTION_PRESS
             
-            // By setting this to non-nil, we note that we'rein a keyDown event. From here,
+            // By setting this to non-nil, we note that we're in a keyDown event. From here,
             // we call interpretKeyEvents so that we can handle complex input such as Korean
             // language.
             keyTextAccumulator = []
@@ -825,6 +825,47 @@ extension Ghostty {
             keyAction(GHOSTTY_ACTION_RELEASE, event: event)
         }
 
+        /// Special case handling for some control keys
+        override func performKeyEquivalent(with event: NSEvent) -> Bool {
+            // Only process keys when Control is the only modifier
+            if (!event.modifierFlags.contains(.control) ||
+                !event.modifierFlags.isDisjoint(with: [.shift, .command, .option])) {
+                return false
+            }
+
+            // Only process key down events
+            if (event.type != .keyDown) {
+                return false
+            }
+
+            let equivalent: String?
+            switch (event.charactersIgnoringModifiers) {
+            case "/":
+                // Treat C-/ as C-_
+                equivalent = "_"
+            default:
+                equivalent = nil
+            }
+
+            guard let equivalent else { return false }
+
+            let newEvent = NSEvent.keyEvent(
+                with: .keyDown,
+                location: event.locationInWindow,
+                modifierFlags: .control,
+                timestamp: event.timestamp,
+                windowNumber: event.windowNumber,
+                context: nil,
+                characters: equivalent,
+                charactersIgnoringModifiers: equivalent,
+                isARepeat: event.isARepeat,
+                keyCode: event.keyCode
+            )
+
+            self.keyDown(with: newEvent!)
+            return true
+        }
+
         override func flagsChanged(with event: NSEvent) {
             let mod: UInt32;
             switch (event.keyCode) {