Add Playwright visual regression coverage

[edehvictor]

Closes #124

Changes

• add Playwright visual regression tests for the checkout flow
• add Playwright visual regression tests for the create payment flow
• add shared E2E fixtures for seeded merchant state, mocked checkout responses, and visual stabilization
• configure Playwright for desktop and mobile Chrome snapshot coverage
• replace the older broad VRT specs with route-level critical-path coverage
• restore persisted create-payment form state needed for stable E2E rendering

Testing

• npm.cmd run test:e2e:update
• npm.cmd run build

Notes

• this branch was pushed as requested, but the repo is not fully CI-clean yet
• the frontend currently has existing build issues outside the Playwright flow, and the E2E font workaround in src/app/layout.tsx still needs a follow-up fix

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[emdevelopa]

resolve conflict