feat(extensions): add Archive and Reconcile extensions to community catalog (#1844)

* feat(extensions): add reconcile and archive to community catalog

* Update extension link text and add changelogs

Normalize extension link text in extensions/README.md (replace `[@stn1slv]` with `spec-kit-archive` and `spec-kit-reconcile`) and add CHANGELOG URLs to the corresponding entries in extensions/catalog.community.json for the Archive and Reconcile extensions.

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Co-authored-by: Stanislav Deviatov <stn1slv@users.noreply.github.com>