docs: document the visual regression suite

[trust01-ctrl]

Overview

This PR documents the existing visual regression suite so contributors understand what it captures, when and how to update a snapshot deliberately, and why snapshots must never be updated just to silence a failure. It adds a dedicated docs/visual-regression.md guide, links it from the docs index and the e2e README, and adds a short pointer in CONTRIBUTING.md.

Related Issue

Changes

📝 Visual Regression Documentation

• [ADD] docs/visual-regression.md

  • Explains what the visual suite covers (which screens/components are captured and what a snapshot represents).
  • Describes how to run the suite and how to review a visual diff.
  • States the deliberate process for updating a snapshot, including reviewing the diff before accepting it.
  • Warns against updating snapshots to silence a failure, and explains what to do instead (investigate the regression, fix the cause, or raise it for review).

• [MODIFY] docs/README.md

  • Adds a link to the new visual regression guide so it is discoverable from the docs index.

• [MODIFY] e2e/README.md

  • Points readers to docs/visual-regression.md for snapshot coverage, update, and review guidance.

• [MODIFY] CONTRIBUTING.md

  • Adds a short note directing contributors to the visual regression docs before changing or updating snapshots.

Verification Results

npm run lint
✅ passed

npm run typecheck
✅ passed

npm test
✅ passed

npm run build
✅ passed

Acceptance Criteria	Status
The documentation explains what the visual suite covers	✅ docs/visual-regression.md describes the captured screens/components and what snapshots represent
It states how to update a snapshot deliberately	✅ Documented run + review + update flow with diff inspection before accepting
It warns against updating snapshots to silence a failure	✅ Explicit warning with the correct investigation-first workflow

Closes #332

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