fix: sync Valentus FOUC paint-hold in head-meta override

[AMDphreak]

Summary

• Mirror Valentus interim adt-fouc-pending paint-hold so DevCentr brand / mermaid / math CSS does not reintroduce refresh settle.
• Keep brand links with the other stylesheets before the hold releases.

Test plan

• Hard-refresh DevCentr docs light/dark: no chrome settle flash.
• Brand tokens still apply on first paint.

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Documentation review — FOUC paint-hold sync

Assessment: The code change correctly restores Valentus interim paint-hold ordering in head-meta.hbs. Documentation was missing upgrade guidance for this pattern.

Docs added/updated (commit 4d24777 on this branch)

File	Change
docs/modules/ROOT/pages/publishing/antora-ui-branding.adoc	New FOUC paint-hold (interim) section: adt-fouc-pending load order, brand CSS placement, upgrade re-sync steps
docs/modules/ROOT/pages/activity-log.adoc	August 2026 entry for this fix
README.adoc	supplemental-ui/ row now mentions paint-hold + preference boot
dark-mode-analysis.md	Notes paint-hold + brand CSS ordering

Codepaths covered

• supplemental-ui/partials/head-meta.hbs — global paint-hold, layered CSS, dark-mode/read-width/font-size preference boot, release script
• valentus-theme upgrade workflow for consumers of the DevCentr supplemental overlay

Knowledge gaps addressed

• Why the page hides briefly on load (interim until Default UI single-pass CSS)
• Where brand CSS must sit relative to paint-hold release (before release script, after valentus visual/read-width/font-size CSS)
• What to re-diff when bumping valentus-theme (upstream paint-hold block + DevCentr brand link)

Gaps not in scope for this PR

• No separate changelog-details/ structure in this repo — org uses activity-log.adoc instead
• README still lacks CI/CD badge (pre-existing; not introduced by this PR)

  

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