fix: recognize function keys F1–F24 when assigning hotkeys (#2157)

keyboardCodeToHotkeyKey had branches for Key*, Digit*, and Numpad* codes
but none for function keys, so KeyboardEvent.code values "F1".."F24"
returned null and the hotkey capture handler silently dropped them. This
made every function key unassignable (not just F13+ such as F21/F22).

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

src/shared/utils/keyboard-code-to-hotkey.ts

@@ -61,6 +61,10 @@ export const keyboardCodeToHotkeyKey = (code: string): null | string => {
         return code.slice(5);
     }
 
+    if (/^F([1-9]|1\d|2[0-4])$/.test(code)) {
+        return code.toLowerCase();
+    }
+
     if (code.startsWith('Numpad')) {
         const suffix = code.slice(6);
         const numpadMapped = NUMPAD_CODE_TO_HOTKEY_KEY[suffix];