Enforce WCAG 2.2 AA conformance as a gated check

[tph-kds]

Specialist professionalism bar: every editable-deck output must meet WCAG 2.2 AA before it is accepted.

Gap: contrast, focus visibility, and reduced-motion fallbacks are documented requirements but not enforced as a gate with detectors + manual checklist.

Acceptance:

• Automated detector for color-contrast failures on text and UI components (based on skills/deckforge/references/chart-accessibility.md and theme tokens).
• Focus-visible indicator detection and keyboard-operability checks for the editor and presenter.
• Reduced-motion fallback detection for every serialized motion profile.
• Human-review checklist item in the delivery acceptance contract for states detectors cannot prove (e.g. reading order, semantics).
• Wired into npm run validate.