Add get_preview and get_preview_image for link unfurling

[Robbie1977]

Slack, Bluesky, Teams and the rest build a link card from the og:* tags in
a page's raw HTML, and none of them run JavaScript. The viewer sets those
tags per term from JS only, so a pasted term link previews as the site logo
whatever the term.

get_preview?id= renders the same tags server-side from get_term_info --
title, description, thumbnail, canonical to /reports/ -- with a
meta-refresh into the viewer so a human landing here still arrives where the
link pointed. Intended for an IRI-routing branch that hands unfurler
user-agents this instead of the redirect.

get_preview_image?id= redirects to the term's thumbnail, or the logo
when it has none: a stable id-keyed image URL for og:image, cards and the MCP.

Both reuse the term_info: cache key, so a preview costs no extra term
lookup and a burst of unfurlers for one link coalesces to one query; the
HTML is a 2KB response v3-cached stores like any other.

Title and description logic mirrors pageMetadata.js in geppetto-vfb so a term
reads the same wherever its preview is built -- except that ';' in Types
becomes ', ' rather than ',', which reads as a list; the JS wants the same fix
on its next release.

Ontology text is HTML-escaped, and ids are validated against the VFB id shape
before any lookup.

[github-actions]

⚠️ 1 test(s) skipped — an upstream data source was unreachable

The full suite ran, but 1 test(s) were skipped because an upstream data source (VFB's Neo4j / SOLR / Owlery, or FlyBase's Chado) did not answer during this run.

These are not failures and not a problem with this branch — but those queries went unverified, so a green check here is an incomplete run.

To re-run: open this workflow run and click Re-run all jobs once the data sources are healthy (re-running the “Run completeness” check itself does nothing — it has no job behind it).

1 failed, 873 passed, 1 skipped, 340 warnings in 1078.55s (0:17:58)

_{Posted automatically. This comment is removed once a run completes with zero skips.}