feat: allow `enabled` to accept a callback for lazy evaluation

Feature Request

Summary

Currently, the enabled option in HotkeyOptions only accepts a boolean. It would be useful to also accept a callback (i.e. () => boolean) to support lazy evaluation.

Motivation

There are cases where the enabled state depends on values that are re-evaluated at hotkey trigger time, not at registration time. Having to re-register the hotkey every time that condition changes is cumbersome.

A callback form would allow users to defer the check to when the hotkey is actually fired:

useHotkeys('mod+s', save, {
  enabled: () => !isReadOnly,
})

Proposed API change

// Current
enabled?: boolean

// Proposed
enabled?: boolean | (() => boolean)

The implementation would just call enabled() instead of reading it directly when it's a function.

Alternatives considered

Passing a reactive enabled value that changes over time works, but requires the caller to manage that reactivity and causes unnecessary re-registrations.

Start at the HotkeyOptions definition for the enabled option and trace where enabled is checked when a hotkey fires. Update the type and runtime handling so boolean and callback forms are supported, then verify that the callback is evaluated at trigger time and that existing boolean behavior remains unchanged.