[tmashara]

Adds a slider view to report.html. A Slider view checkbox at the top of the sidebar swaps every card's left / right / diff grid for both shots stacked, tops aligned (the taller side's extra rows show below), with a divider that reveals left on one side and right on the other.

• The toggle is CSS only (body:has(#slide:checked)). The grid stays the default and nothing is persisted. Lazy images in the hidden view aren't loaded until it's shown.
• The divider is a full-height, transparent <input type="range"> over the stack, so a drag can start anywhere on a tall shot. Keyboard arrows work, and focus shows as an outline on the slider. Two lines of inline JS copy its value into --x, which drives clip-path on the left shot and the divider line.
• The slider adds no <a href>, so a card still links exactly its three images.
• Known limit: both shots are scaled to the card width, so a shot with a width delta doesn't line up in the slider (the width badge and the diff image still show it).
• evidence.html is unchanged: its CSP blocks script, and it shows only crops.

Fixes #43

Verification

• npm run typecheck, npm run lint, npm run format:check: clean
• npm test: 358/358, including a new writeReport test for the toggle and slider markup and the three image links
• npm run test:visual: 389/389
• Manual check in Chromium on a report generated from the fixture site (/taller, /shifted, /color):
  • Dragging from low down on a 2,900px-tall slider moves the divider and clips the left shot.
  • Clicking anywhere jumps the divider there, and arrow keys move it.
  • The wheel still scrolls the page over the slider, focused or not.
  • Unticking the toggle restores the grid.
  • The filter box keeps its styling and the checkbox isn't stretched.

🤖 Generated with Claude Code