chrismwilliams/astro-theme-cactus ? reverse-engineered prompt

Build me a clean personal blog and website using this Astro Cactus theme. I want it to feel simple, fast, and polished, with a nice light and dark mode, good mobile layout, readable typography, and solid SEO so it looks good when shared.

Set it up so I can easily add blog posts, short notes, and tag pages from Markdown or MDX, and make sure the homepage, post pages, tag pages, and about style content all fit together nicely. I’d also like the built in search, RSS feed, sitemap, robots file, social sharing image support, and the small extra touches like code block styling and icons to work out of the box.

Please make the starter easy to customize too, so I can swap in my own site name, colors, logo, social links, and content without having to dig around too much. If anything needs current docs or a quick check online, feel free to look it up.