Add changelog extension (#2177)

* Add Spec Scope extension to community catalog

Adds spec-kit-scope: effort estimation and scope tracking from spec artifacts.

4 commands:
- /speckit.scope.estimate — data-driven effort estimation with three-point ranges
- /speckit.scope.compare — side-by-side spec scope comparison
- /speckit.scope.creep — scope creep detection via git history
- /speckit.scope.budget — sprint-ready time budget generation

1 hook: after_specify (auto-estimation)

Turns "how long will this take?" into a data-driven answer.

* Add Spec Changelog extension to community catalog

* Add Spec Changelog extension to community catalog

* fix: drop accidental scope entry, restore Intelligent Agent Orchestrator README row, return Spec Reference Loader to original position

Per Copilot review on PR #2177: this branch is supposed to add only the
Spec Changelog extension. The diff against main also showed (1) a duplicate
'scope' catalog entry, (2) a deletion of the Intelligent Agent Orchestrator
README row, and (3) Spec Reference Loader moved out of alphabetical order.
All three were merge artifacts and have been cleaned up here.

* Potential fix for pull request finding

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

* fix: keep Spec Changelog row alphabetically sorted

Address Copilot review on PR #2177: the Community Extensions table is
sorted alphabetically by display name, and 'Changelog' precedes 'Critique',
'Diagram', 'Orchestrator', and 'Reference', so the Spec Changelog row
belongs right after Ship Release Extension. Move it into its sorted slot
and keep Spec Reference Loader in its original alphabetical position
(between Spec Orchestrator and Spec Refine).

* fix: remove duplicate Spec Reference Loader row from README

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

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Co-authored-by: Manfred Riem <15701806+mnriem@users.noreply.github.com>
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>