fix: enable GitHub Pages for pkgdown site

[bbuchsbaum]

Summary

The pkgdown workflow was building and deploying successfully to gh-pages, but GitHub Pages was never enabled (has_pages: false), so https://bbuchsbaum.github.io/templateflow/ returned a GitHub 404.

Fix

Smallest coherent change, matching sibling portfolio packages (neuroim2, bidser):

• Grant pages: write on the pkgdown job
• Add an Enable GitHub Pages step that POSTs {"source":{"branch":"gh-pages","path":"/"}} (idempotent via || true) before deploy

No package semantics, tests, or other CI gates were changed.

Evidence

• Live URL before fix: HTTP 404 (“There isn't a GitHub Pages site here”)
• Repo API: has_pages: false while gh-pages already contains a valid pkgdown index.html
• Workflow YAML validated locally
• After merge to main, the push-triggered pkgdown job should enable Pages and redeploy; the portfolio monitor should then see a live site

Remaining blocker

If org/repo Actions permissions disallow creating Pages via GITHUB_TOKEN even with pages: write, an admin must enable Pages once under Settings → Pages → Deploy from branch gh-pages / root. The workflow change is still the correct durable fix.

  

[bbuchsbaum]

Independent review: the pkgdown artifact and gh-pages branch were already valid; GitHub Pages itself was disabled. Pages has now been enabled directly from gh-pages:/, the deployment succeeded, and https://bbuchsbaum.github.io/templateflow/ returns HTTP 200. This workflow change is therefore unnecessary. In addition, || true would conceal authorization or API failures and could leave a green workflow with a broken site. Closing unmerged.