[scanner] site: tag-filtered indexes (/tags/<tag>/)

[kubestellar-hive]

Adds two new statically-generated page templates and makes existing TagChip components clickable so a reader mid-incident with their RAG pipeline at 3am can click evals on an issue page and land on every featured-eval item across every issue.

Pages

• /tags/ — landing page. Enumerates every distinct tag encountered on any featured item with an occurrence count. Sorted by count desc, then alpha.
• /tags/<tag>/ — every featured item carrying <tag>, sorted date desc, then score desc. Shows title (linking to source), date (linking to /issues/<date>/), section, source, score bar, and summary excerpt.

Implementation notes

Straight from the issue:

• Uses getCollection("issues") and flattens featured[].tags to drive both getStaticPaths() and the counts on /tags/.
• Tags are the closed 13-tag vocabulary from the ranker prompt, but routing is data-driven — any tag that appears on a featured item gets its own page. Defensive against future vocabulary growth.
• Appendix items intentionally excluded (they carry no tags — only featured items get the editorial treatment that includes tagging).
• Hyphenated tags (tool-use, cost-latency) round-trip through Astro's default routing without URL encoding gymnastics.
• Light + dark modes use existing --border / --accent CSS variables — no new theme tokens.

TagChip

Now a link by default (<a class="chip chip--link">). Callers that need a plain span (e.g. inside a larger clickable container) can pass static — no such caller exists today but the escape hatch is there.

Verification

Ran astro build locally against the existing test issue. Output:

• /tags/agents/index.html generated with the featured item listed and score bar rendered.
• /tags/index.html generated with agents (1) link.
• Issue-page chips render as <a class="chip chip--link" href="/tags/agents/">agents</a>.

Pitfalls addressed

• Statically generated at build time — no runtime computation.
• Hyphenated tags round-trip cleanly.
• No appendix leakage.

Fixes #7

[github-actions]

Coverage report

This PR does not seem to contain any modification to coverable code.