chore: update manifest to 3.0.0

[github-actions]

Manifest update

Version: 2.1.0 → 3.0.0 (major)

Changelog

• aux_uncertainty_id: new collection model
• has_aux_unc: new collection model
• nominal_resolution: updated collection model
• site_id: new collection model
• site_location: new collection model
• source_id: updated collection model
• _CVs: 12 removed
• activity_id: 1 modified
• aux_uncertainty_id: 9 added
• conventions: 1 added
• frequency: 4 modified
• grid_label: 2 added
• has_aux_unc: 2 added
• institution_id: 19 added, 32 modified
• nominal_resolution: 19 added, 1 modified, 14 removed
• realm: 4 modified
• site_id: 267 added
• site_location: 1 added
• source_id: 136 added, 22 modified
• source_type: 1 added

---

Once merged, publish the release:

gh workflow run publish.yml \
  -R WCRP-CMIP/esgvoc_registry \
  -f project_id=obs4ref \
  -f bump_type=major \
  -f project_repo=Climate-REF/Obs4REF_CVs

[github-actions]

Release preview

No CV files changed — no release needed.