fix(ci): Allow leading digit in kebab-case filename rule

The kebab-case Danger rule required the filename stem to start with a
letter, so a legitimately kebab-cased, date-prefixed name like
2026-06-13-backend-review.md failed — and the rule's own suggestion was a
no-op (it suggested the identical name). Kebab-case permits digit-led
segments (dates, 2fa-setup, …); relax the stem regex to
/^[a-z0-9]+(-[a-z0-9]+)*$/ and restore the original review filename.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: enko

docs/reviews/backend-review-2026-06-13.md docs/reviews/2026-06-13-backend-review.mddocs/reviews/backend-review-2026-06-13.md renamed to docs/reviews/2026-06-13-backend-review.md

@@ -2,7 +2,10 @@ import * as path from 'path';
 import type { DangerRule } from '../types';
 import { isExemptFile, isIgnoredPath } from '../utils';
 
-const KEBAB_CASE_STEM = /^[a-z][a-z0-9]*(-[a-z0-9]+)*$/;
+// Lowercase alphanumeric segments separated by single hyphens. A segment may
+// start with a digit so date-prefixed names (e.g. 2026-06-13-backend-review)
+// and names like 2fa-setup are valid kebab-case.
+const KEBAB_CASE_STEM = /^[a-z0-9]+(-[a-z0-9]+)*$/;
 
 // Migration files use a "<timestamp>_<name>" pattern — strip the prefix before checking
 const MIGRATION_PREFIX = /^\d+_/;