Make hotkeys work reliably in the pop-out window

[rahul-muthu]

What changed

Hotkeys could stop working when the pop-out timer window had focus.

The pop-out window now forwards keyboard input to the existing browser hotkey handler. This includes modifier keys and numpad keys. The handler is connected as soon as the pop-out opens, so shortcuts also work while the window is still loading.

Desktop hotkeys are left unchanged because they are already global, and adding another listener there could trigger commands twice.

Testing

• Opened the timer and popped it out into a separate window
• Focused the pop-out and used Numpad1 to start the timer
• Confirmed the timer continued updating
• Ran TypeScript checks
• Ran ESLint
• Completed a production build