test: visual regression snapshots for wallet/transaction/network modal breakpoints

[nottherealalanturing]

Introduced a dedicated VisualTestHarness wrapper to deterministically render critical modals (Wallet, Transaction) across multiple predefined viewports (MOBILE, TABLET, DESKTOP) and themes for accurate Playwright/Storybook snapshot testing.

Highlights:

• Created VisualTestHarness component in src/features/visual-testing/VisualTestHarness.tsx
• Created custom hook useVisualTestHarness in src/features/visual-testing/useVisualTestHarness.ts
• Added Zustand store in src/features/visual-testing/visualTestingStore.ts
• Created types in src/features/visual-testing/visualTestingTypes.ts
• Wrote extensive unit tests in src/features/visual-testing/VisualTestHarness.spec.tsx

close #665
close #664
close #663
close #662

[nanaf6203-bit]

LGTM