owner-led(visual-agent): Playwright before/after capture across viewports

[JSONbored]

Parent roadmap: #525
Parent epic: #577

Owner-led — assigned to @JSONbored.

Goal

Playwright capture: screenshot each affected route at one or more viewports (desktop/mobile), for both base and head → before/after image pairs.

Reuse

The existing Playwright browser harness (scripts/smoke-ui-browser.mjs, test:smoke:browser).

Scope

• Headless capture with hydration-wait + network-idle.
• Configurable viewports; deterministic settling (disable animations, freeze time/fonts).
• Output before/after PNG pairs per route+viewport.

Acceptance

For a set of routes, produces matched before/after PNGs that are stable across runs.

[JSONbored]

Closing as not planned (2026-07-01 issue audit): Multi-viewport before/after capture already shipped in shot.ts (DESKTOP/MOBILE viewports, #1056).