docs: close out Scient rename

[yaacovcorcos]

Summary

• make Scient the active product and repository identity across current documentation, indexes, skills, and lab paths
• record the verified scient-desktop and scient-agent source merges and preserve PapiLab only for migration/history
• distinguish the owned scient-agent source repository from the still-unimplemented native Scient runtime
• keep the public website cutover explicitly owner-deferred

Verification

• git diff --check
• zero broken relative Markdown links across tracked documentation
• active naming audit found no ScientFactory/opencode, stale pre-execution wording, or old local checkout directories
• source PRs merged green: scient-desktop Remove obsolete icon references #12 (d9d8992a) and scient-agent docs: finish governance cleanup #6 (5ffaf9a2)

Local preservation

• preserved the pre-existing dirty desktop user branch without reset or content changes while renaming its checkout directory