## Why

Recent regressions in color accessibility and tooltip behavior show that current automated checks are not broad enough to catch cross-theme, cross-state UI/UX defects before release. We need deterministic browser-level coverage that validates real user journeys and interaction states across the full product surface.

## What Changes

- Add a Playwright-based UI/UX regression suite that runs against the real frontend and API.
- Define a complete test strategy covering all shipped capabilities, including themes, localization, accessibility, modal flows, permalink deep-links, footer controls, and sharing interactions.
- Add scenario-driven test cases for all component states (default, hover, focus, active, visited, disabled where applicable) and breakpoint behavior.
- Add visual and interaction assertions for hero/feed rendering, policy modals, summary modal actions, and tooltip behavior.
- Integrate the Playwright suite into quality gates with clear pass/fail policy and reporting.

## Capabilities

### New Capabilities
- `playwright-ui-ux-regression-suite`: Browser-automation test architecture, coverage matrix, and deterministic execution model for full UI/UX regression prevention.

### Modified Capabilities
- `end-to-end-system-testing`: Expand requirement scope to include browser-native UI/UX scenarios and state coverage.
- `platform-quality-gates`: Add Playwright execution and failure gating into CI quality stages.
- `wcag-2-2-aa-accessibility`: Add automated browser assertions for contrast, focus visibility, keyboard navigation, and accessible names/labels in real interactions.
- `responsive-device-agnostic-layout`: Add breakpoint-aware UI regression scenarios for desktop/tablet/mobile including sticky header/footer and floating controls.
- `summary-modal-experience`: Add modal interaction regression scenarios (open/close, escape, focus behavior, source CTA/share actions).
- `share-and-contact-microinteractions`: Add deterministic test coverage for share actions and contact tooltip behavior across pointer and keyboard interactions.

## Impact

- Affected code: test infrastructure, frontend E2E test files, CI workflow definitions, and test documentation.
- Affected systems: CI quality gate pipeline and release confidence checks.
- Dependencies: Playwright runtime/browsers and supporting test fixtures.
- Operational impact: Longer CI runtime offset by significantly improved regression detection for UI/UX defects.