Emit og:image from page cover

grep 'property="og:image"' build/**/index.html finds only og:image:type, og:image:width, og:image:height and og:image:alt. The actual og:image and twitter:image are never emitted, even for feature pages that define cover in their meta.

This is separate from dynamic OG image generation: even without generated images, the existing cover should be published.

Cause

• Meta.svelte derives coverUrl from its cover prop; the root layout renders <Meta /> without props
• getPageInfo() in pages.remote.js returns title, description, tags, etc. but not cover
• The emitted og:image:type is hardcoded to image/png and 1200x630 regardless of the real cover

Tasks

• Return the cover's largest img.src (absolute, via PROJECT_URL) from getPageInfo()
• Use it in Meta.svelte for og:image and twitter:image; only emit type/width/height when known
• Fall back to a static site-wide OG image for pages without a cover
• Add a build-time test that every listed page has an absolute og:image