Brand Kit Page and Footer Contact Email

Added /site/design as a proper brand kit page — colour tokens, font stack, the pentacle mark, the seasonal palette system. Mostly for my own reference so I stop second-guessing whether something is --primary-500 or --accent-400 mid-build. Also makes it easier to document the Wheel of the Year interpolation visually, given how much of the site's identity is wrapped up in it now.

Also added a contact email to the footer. It was conspicuously absent, which seemed like an oversight — the Ko-fi commissions and GitHub Sponsors are both open, and people shouldn't have to find me on witchsky.app just to ask about a project or a commission. The footer was already linking to the support page; this just adds the direct line.