feat(website): add diff view for comparing sequence versions

[corneliusroemer]

Based on quick vibe code session with @maverbiest

First attempt at offering some diffing between versions - we have nothing so far. This is better than nothing - clearly has room for improvement.

Try it out:

• Sequences with 2 versions show diff automatically: https://diff-versions.loculus.org/seq/LOC_0002GVP.2/versions?compare=1%2C2
• Sequences with more than 2 allow selecting 2 to diff: https://diff-versions.loculus.org/seq/LOC_0002H0D.4/versions?compare=2%2C4

Summary

Add interactive diff view to compare metadata changes between sequence versions on the /seq/{accession}/versions page.

Features

• Smart defaults: Auto-compares when only 2 versions exist, shows checkboxes for 3+ versions
• URL persistence: Shareable links with ?compare=1,3 format
• Toggle view: Show all fields or only changed fields
• Noisy field handling: Timestamps and version info displayed greyed out at bottom
• Visual design: Changed fields highlighted with amber background, grouped by metadata headers

Components

• VersionsWithDiff.tsx - Main React component with version selection and data fetching
• DiffTable.tsx - Table display with field comparisons
• compareVersions.ts - Logic to identify changed/unchanged/noisy fields
• types.ts - TypeScript types for comparison results

Test Plan

• Type checking passes (npm run check-types)
• Unit tests pass (CI=1 npm run test)
• Code formatted (npm run format)
• Manual test: Browse to a sequence with 2 versions on preview, verify auto-compare
• Manual test: Browse to a sequence with 3+ versions, select 2, verify comparison
• Manual test: Toggle "Show all fields", verify unchanged fields appear
• Manual test: Verify URL params persist and are shareable
• Manual test: Verify noisy fields (timestamps) are greyed out

🤖 Generated with Claude Code

🚀 Preview: https://diff-versions.loculus.org

[anna-parker]

@anna-parker tetsing notes:
Navigated to a sequence with multiple versions: https://diff-versions.loculus.org/seq/LOC_0002H0D.4

Display name and Annotations should not be highlighted - potentially lets completely remove the annotations.

certain fields are shown even if they do not change on each comparison view (e.g. the NCBI release date at the bottom):

however, other fields that do not chnage (e.g. sequence details are not shown on default view as desired)

I can select 2 different versions to compare, the compare urls persist and are sharable.