feat(site): make testbed results easier to read

[yschimke]

Summary

• lead with a verdict, coverage, release-to-snapshot comparison, and endpoint health derived from the published result data
• make the suite matrix searchable and filterable, and add clearer version and history summaries
• generate in-page navigation from each page’s headings and improve responsive layout, tables, and dark mode

Live-data review

Validated the presentation against the currently deployed result payload:

• 1,356 / 1,427 checks ran
• 142 shared suites had aligned outcomes
• 21 / 22 public endpoints were reachable

These values are not hard-coded; they are examples of what the new presentation derives from latest.json.

Verification

• node --check site/assets/status.js
• node --check site/assets/navigation.js
• node --test site/assets/finding-groups.test.js
• python3 -m compileall -q site/tools
• HTML script-reference and duplicate-ID check
• git diff --check