fix(templates): Pages geometry accounts for subgroup nesting
What
The docs starter's astro.config.mjs bakes in https://<GROUP>.gitlab.io + base: /<PROJECT_NAME> — wrong for any project nested in a subgroup. GitLab Pages serves at the ROOT namespace's domain with the full remainder as the path: group/subgroup/project serves at https://group.gitlab.io/subgroup/project/.
How it surfaced
public-sector/egress (stamped from this template before the scaffold-script retirement) shipped with base: '/egress' and the malformed site URL https://gitlab-com/public-sector.gitlab.io. Every subpage 404d on Pages. Fixed instance-side in egress; this MR fixes the source so the next adaptation cannot repeat it.
Fix
Two documented placeholders replace the old pair wherever Pages URLs appear in the lab and docs starters:
<PAGES_ROOT_NAMESPACE>— first segment of the group path (the Pages domain).<PAGES_BASE_PATH>— subgroup nesting plus project slug, leading slash (/public-sector/egress;/<project>for an un-nested group).
Both README-template placeholder tables document the derivation for adapters following the SSOT map. scripts/validate-templates.sh and just check pass (18 standards).