Lint: validate decisions-index against all decisions-index Feature REQs

[trakhimenok]

Summary

Add lint rules that validate spec/decisions/README.md (active decisions index) and spec/decisions/archived/README.md (archived decisions index) against every REQ in the decisions-index Feature (Status: Approved).

Source

• Feature: decisions-index (Approved)
• Plan: Decision CLI Implementation — Task 5, Issue D
• Scenario stubs: spec/features/decisions-index/_tests/

Rules to implement

Rule	REQ	Scenario stub	Auto-fix?
List section must use heading `## Decisions`	list-section-heading	wrong-list-section-heading-rejected	No
Table must include columns #, Decision, Status, Date, Tags, Affected (in order)	index-columns	missing-index-columns-rejected	No
No Superseded/Deprecated rows in active index	status-excludes-archived	archived-decision-in-active-index-rejected	No
Rows in ascending numeric order by #	numeric-ordering	out-of-order-rows-rejected	Yes — lint --fix reorders
Archived index in chronological order by Date	archived-index-chronological	archived-index-out-of-order-rejected	Yes — lint --fix reorders
Adherence footer with correct URL	adherence-footer	missing-adherence-footer-rejected	No

Also inherits shared Index rules from the Index Feature: completeness (every active Decision has a row), required sections minimum, adherence-footer delegation.

Dogfood fixture

The current spec/decisions/README.md in specscore/specscore has been updated to match the specified column set and must pass all new rules without modification.