Add themes page

[tahayvr]

This PR adds a Themes page to the site. This will replace the "Extra Themes" page in the Omarchy Manual.

• New themes.json includes data for the extra themes made by community.

// sample entry
{
    "name": "VHS 80",
    "author": "tahayvr",
    "type": "dark",
    "primary_colors": ["red", "yellow", "green"],
    "repo_url": "https://github.com/tahayvr/omarchy-vhs80-theme",
    "preview_url": "https://raw.githubusercontent.com/tahayvr/omarchy-vhs80-theme/main/preview.png"
  },

• New themes page and themes.js that gets the themes data from themes.json.

I didn't add a button for this page in the Homepage nav to avoid conflicts but can do it once this is approved.

[omarchybot]

Heads up that master has since shipped a themes gallery at this same path, so this pull request as it stands would collide with it rather than add to it.

themes/index.html landed on master on 2026-08-14 in 21cb529, "Add the extra themes gallery at themes/", and has been grown by community pull requests since — it now lists 126 themes as static HTML with the previews committed locally as optimised webp. Both themes/index.html and assets/css/themes.css are add/add conflicts against it.

Comparing the two sets by repository URL: 63 of this PR's 65 themes are already on master. The two that are not are Bliss (mishonki3/omarchy-bliss-theme) and Flexoki Light (euandeas/omarchy-flexoki-light-theme). Those are the only content here that master does not already have, and they would be welcome as a small pull request against the gallery that exists — that is a much easier review than this one, and it is the part of this work that is not duplicated.

Three things worth recording while this is open, in case the approach ever comes back:

• 64 of the 65 preview_url values in themes.json hotlink raw.githubusercontent.com, so the gallery would depend on 64 third-party repositories keeping those files in place. Master's gallery commits the previews instead.
• Entry 57, "Synthwave '84", has preview_url set to the empty string, so it would render an <img> with no source. Every other entry has one.
• themes/index.html:163 is <div/> where </div> was meant. HTML does not self-close a non-void div, so the parser reads it as another opening tag and the .nav container never closes — <main> and the footer end up nested inside the navigation. The file has 13 opening div tags against 11 closing ones.

Nothing here is a criticism of the work — it sat for seven months and the site moved. Deciding whether to close it is the maintainer's call, not mine.