Add Royal Kludge RK61

[DEREFERENC3D]

Description

Adds support for the RK61. Based on the OEM-provided config file, cleaned up and updated to match the keyboard's definition in mainline QMK.

QMK Pull Request

qmk/qmk_firmware#25694

VIA Keymap Pull Request

the-via/qmk_userspace_via#118

Checklist

• The VIA support for this keyboard is MERGED in QMK master already (MANDATORY)
• VIA keymap is MERGED in VIA userspace master already (MANDATORY)
• The VIA definition follows the guide here: https://caniusevia.com/docs/layouts
• I have a V3 JSON version for this keyboard definition.(MANDATORY)
• I have formatted the JSON file to have consistent formatting with the rest of the repository.
• I have tested this keyboard definition using VIA's "Design" tab.
• I have tested this keyboard definition with firmware on a device.
• I have assigned alpha keys and modifier keys with the correct colors.
• The Vendor ID is not 0xFEED

[Cipulot]

@DEREFERENC3D mark ready when needed

[DEREFERENC3D]

@Cipulot Sorry, I got a little busy and kind of forgot about this PR. I've gone through the guide and done a quick re-test after upgrading to the latest mainline QMK, it should be ready. I am only unsure about the alpha, modifier and accent key colors, but I guess that will come out in review - for now I'm keeping the OEM-provided values, which match the single-color stock keycaps.