fix(docs): deploy the docs site for this fork, not upstream's domain

[Elektr0Vodka]

What changed

• .github/workflows/github-pages.yml: drop cname: docs.meshcore.nz. Every deploy wrote upstream's custom domain into gh-pages as a CNAME file.
• mkdocs.yml: site_name, site_url, site_description, repo_name and repo_url now point at this fork (elektr0vodka.github.io/meshcomod) instead of meshcore-dev.
• docs/index.md: the Documentation Source link points at this repo.
• changelog_ev.md: entry for the fix, and PR numbers on the docs: add fork changelog, README fork status and docs dark theme #11 entries.

Why

The mkdocs site (with the dark theme from #11) never showed on https://elektr0vodka.github.io/meshcomod/. Pages is set to serve main /docs through Jekyll, so the mkdocs output on gh-pages is ignored. Pointing Pages at gh-pages while that branch carries upstream's CNAME would move the site to docs.meshcore.nz, so the CNAME has to go first.

After this merges and the workflow redeploys gh-pages without the CNAME, the Pages source needs to be switched to the gh-pages branch, root folder (repo setting, not part of this diff).

Testing

• mkdocs build succeeds; the output has no CNAME and the canonical URL is https://elektr0vodka.github.io/meshcomod/.

Firmware or build impact

None. Docs site config only.