feat: configurable hotkey binding and ModifierKeyTracker

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

Sources/SstCore/HotkeyMonitor.swift

@@ -6,13 +6,18 @@ public final class HotkeyMonitor {
         case tapUnavailable
 
         public var errorDescription: String? {
-            "Kan de Fn-toets niet volgen: geef Input Monitoring-rechten in Systeeminstellingen en probeer opnieuw (soms is een herstart van de app nodig)."
+            "Kan de sneltoets niet volgen: geef Input Monitoring-rechten in Systeeminstellingen en probeer opnieuw (soms is een herstart van de app nodig)."
         }
     }
 
     public var onEvent: ((HotkeyEvent) -> Void)?
 
-    private var tracker = FnKeyTracker()
+    /// The key that has to be held. Changing it resets the press tracking.
+    public var binding: HotkeyBinding = .fn {
+        didSet { tracker = ModifierKeyTracker() }
+    }
+
+    private var tracker = ModifierKeyTracker()
     private var tap: CFMachPort?
     private var source: CFRunLoopSource?
 
@@ -56,10 +61,10 @@ public final class HotkeyMonitor {
         case .tapDisabledByTimeout, .tapDisabledByUserInput:
             if let tap { CGEvent.tapEnable(tap: tap, enable: true) }
         case .flagsChanged:
-            // .maskSecondaryFn is also set while arrows/F-keys are held; only react to the Fn key itself.
-            guard event.getIntegerValueField(.keyboardEventKeycode) == 63 else { return }
-            let fnDown = event.flags.contains(.maskSecondaryFn)
-            if let hotkeyEvent = tracker.process(fnDown: fnDown) {
+            // Flags are shared between left and right keys and with arrows/F-keys: only react to the bound key itself.
+            guard event.getIntegerValueField(.keyboardEventKeycode) == Int64(binding.keyCode) else { return }
+            let isDown = event.flags.contains(binding.flag)
+            if let hotkeyEvent = tracker.process(isDown: isDown) {
                 onEvent?(hotkeyEvent)
             }
         default: