Add Open Graph/title meta tags to viewer index.html

[fmigneault]

Problem

The viewer shell's index.html (generated in validate-and-process.yml, "Deploy Building Blocks viewer" step) had a hardcoded <title>OGC Location Building Blocks</title> and no Open Graph / Twitter meta tags.

Link preview/rendering cards (Slack, Discord, Twitter/X, etc.) fetch the raw HTML without executing the SPA's JS, so every register deployed via this workflow showed the same generic title in link previews, regardless of the register's actual content (e.g. a STAC building block register showed "OGC Location Building Blocks" instead of something reflecting STAC).

The browser tab title was unaffected since bblocks-viewer sets document.title dynamically via JS after the SPA loads.

Fix

Populate <title>, og:title/og:description/og:url/og:type, twitter:card/title/description, and name=description from the register's name/description (falling back to abstract), HTML-escaped for safety.

Scope / limitations

This fixes the register root landing page card. Per-block deep links within the SPA still can't get distinct link previews without SSR/prerendering, since a client-side-only SPA can't serve different static meta per route.

[avillar]

Thanks for this, I like it a lot. One question: should we use description or just abstract? Description is intended to be longer, and it'll possibly contain different paragraphs and such, which may not be all that well suited for a meta tag. IMHO, the abstract is much better for this...

[fmigneault]

I don't think abstract is very widespread compared to description field. It implies using extra profile details according to https://www.w3.org/TR/html401/struct/global.html#h-7.4.4, such that it is registered as known term.

It doesn't look like abstract is part of HTML5 either, but description is (https://html.spec.whatwg.org/multipage/semantics.html#standard-metadata-names).

Similarly, Open Graph defines the title/description, but not abstract.

I would keep description for consistency between versions.

[rob-metalinkage]

Looks ok to me. But i am not in the weeds of HTML these days so only looking at requirements and logic.