Seed Compare with useful image pairs - #70

What changed

• automatically seed a blank Compare route with the latest canonical nightly image pair that is actually present in Perf/Eval filters
• add one-click presets for the latest nightlies and latest official releases
• keep explicit deep links and a user's cleared selections authoritative
• replace long registry references with concise release/nightly labels while preserving raw values for search and tooltips
• preserve date filters in the URL and fix the image-detail card's narrow-screen overflow
• add focused tests for pair selection and label formatting

Why

Compare previously opened with two empty selectors, so users first had to understand opaque registry tags and manually hunt for a compatible pair before seeing any result. The default now opens on a real comparison with 73 matched checks while keeping every filter editable.

Visual

Validation

• npm test — 7/7 passing
• targeted ESLint — passing
• npx tsc --noEmit — passing
• npm run build — 43 routes generated
• visual inspection in light mode at 1440px and a true 390px emulated viewport
• verified the default pair returns 73 matched checks (63 perf, 10 eval)