ci: fxcss 0.23.0 — previews validate screenshots and cover new variants

[adamXbot]

Moves the four fxcss workflows from fxcss 0.21.0 to 0.23.0. I regenerated them with fxcss init --watch --previews --force, then re-applied this repo's two edits to firefox-watch.yml:

• --strict-vars on the audit, with the note on why it's safe without an ESR job.
• The #placesToolbar → #PlacesToolbar lesson in the folded-output comment.

To confirm those were the only local edits, I regenerated with 0.21.0 and compared against master. Nothing else differed, and pr-preview-cleanup.yml is unchanged.

What changes

• pr-preview-publish.yml
  • Variant previews are matched by a bounded name pattern (variant-[a-z0-9][a-z0-9+-]{0,159}) instead of the hard-coded list of 30 variants. A new variant such as the Monterey one in feat: Monterey variant (one-line compact layout), installable via -m (#41) #194 gets previews without regenerating this file. All 30 current names still match.
  • Every screenshot is checked as a real PNG (signature, IHDR, size limits) before it's published.
  • The comment now flags unreviewed screenshots and views missing from the PR's captures.
  • An unreadable summary or an empty report now fails the run instead of posting a misleading comment.
• pr-preview.yml
  • Also runs for optional/, options/, extras/ and variants/ changes.
  • On Linux, it waits for Xvfb to be ready and fails clearly with its log if it isn't.
• firefox-watch.yml
  • Manual runs choose the channel from a dropdown (all/release/beta/nightly).
  • The issue and PR steps only act when the audit or capture step actually ran.
• readme-previews.yml
  • Also runs on configuration/ changes.
  • The variant crops are copied safely when none exist.

Every workflow passes actionlint and parses as YAML. This PR changes pr-preview.yml, so the preview workflow runs on it, which tests the new version for real.

🤖 Generated with Claude Code

[github-actions]

Theme preview

Rendered from cf494d3 against the base branch.

Linux — no visual change

Nothing rendered differently. Current appearance:

macOS — no visual change

Nothing rendered differently. Current appearance:

Windows — no visual change

Nothing rendered differently. Current appearance:

No pixel differences on any platform — this PR does not change how the browser chrome renders in these views.

_{Views: browser window, focused address bar, find bar, modal dialog — each in light and dark. Native popups (app menu, context menus) are OS-level windows and cannot be captured. Workflow run}