feat(enrichment): accessibility regression detector analyzer

[JSONbored]

New REES local analyzer (the #1499 epic 'accessibility and i18n regression' idea, a11y half) that flags common accessibility regressions in added JSX/HTML lines: without alt, interactive onClick on a non-interactive element without role/keyboard handler, missing form label association, and positive tabindex. Pure compute over added lines in .jsx/.tsx/.html/.vue, no network.

Deliverables

• Add A11yFinding ({ file, line, rule: 'img-alt'|'click-events-have-key-events'|'label-control'|'positive-tabindex' }) + a11y? key to review-enrichment/src/types.ts
• Create review-enrichment/src/analyzers/a11y-regression.ts: match the four rules on added markup lines only; cap with maxFindings
• Register a local descriptor (category 'quality', cost 'local', requires ['files']) with inline render() in review-enrichment/src/analyzers/registry.ts
• Add review-enrichment/test/a11y-regression.test.ts covering each rule, a compliant element not flagged, non-markup file skip, and the cap

References

• review-enrichment/src/analyzers/iac-misconfig.ts (line-rule local pattern-matcher template)
• review-enrichment/src/analyzers/registry.ts:303-319
• gh issue 1499 lists 'Accessibility and i18n regression detector' as a later idea (this bounty is the a11y half)

Part of #1499.

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size: S · gittensor:feature

[linear-code]

JSO-2143