Add Colemak keyboard layout support

[niklasmarderx]

What

Add Colemak as an alternative keyboard layout alongside the existing QWERTZ/QWERTY layouts.

Why

Colemak is one of the most popular alternative layouts, especially among programmers. Supporting it would make KeyboardWriter useful for a larger audience.

How

1. Look at src/domain/models/KeyboardLayout.ts for how layouts are defined
2. Add a new Colemak layout with the correct key positions
3. Update the VirtualKeyboard component in src/components/keyboard/VirtualKeyboard.ts to render it
4. Add a layout selector in the settings (src/components/settings/SettingsModal.ts)
5. Reference: Colemak layout

Acceptance Criteria

• Colemak layout renders correctly on the virtual keyboard
• Finger assignments are correct for Colemak
• Layout can be switched in settings
• Existing QWERTZ/QWERTY still work