Problem

Theme changes, dark mode, and CSS variable plumbing are easy to break without anyone noticing until users report. Playwright smoke tests cover lifecycle but not visual fidelity.

Proposed approach

• Add Playwright `toHaveScreenshot()` snapshots for:
  • Title bar in light mode
  • Title bar in dark mode
  • Settings modal (light + dark)
  • 1, 2, 3 pane layouts
• Run on the CI matrix; fail on visual diff > 0.5%.

Files to touch

• `tests/smoke/visual.spec.js` (new)
• `playwright.config.js` — snapshot threshold

Acceptance criteria

• CI fails when a visual diff exceeds threshold.
• Updating snapshots is one command: `npm test -- --update-snapshots`.