feat: auto-cleanup visual tracer overlays on page navigation

[ntegrals]

Summary

Visual tracer overlays (click highlights, scroll indicators, etc.) persist across page navigations because they're removed by timeouts that get cancelled when the page unloads. This leaves stale overlay elements or causes visual artifacts on the new page.

Fix

Added attachAutoCleanup(page) method that listens to framenavigated events and automatically calls clearOverlays():

const tracer = new VisualTracer();
const detach = tracer.attachAutoCleanup(page);

// Overlays now auto-clear on navigation
await tracer.highlightElement(page, '#btn', 'Click');
await page.click('#btn'); // navigates → overlays cleaned up

// Detach when done
detach();

Returns a cleanup function to remove the listener when the tracer is no longer needed.

Test plan

• bun run build — compiles clean
• bun run test — all 364 tests pass