Trigger by location changes

To support SPA-like page, the actual impl. launches an observer at a non-target page, detects a change of page contents, then triggers OCR scanner. Obviously, this approach is not robust.

Use location changes for trigger, instead of observing page changes.

Locate the implementation that launches the observer on a non-target page and triggers the OCR scanner after page-content changes. Replace the page-content observation trigger with location-change detection, then verify that navigation to the target page starts scanning without relying on content changes.

Written by the indexing model from the issue text.