feat: per-repo social metadata — SSR share pages + dynamic OG images

Crawler-visible metadata for /repos/:owner/:name without turning the SPA
into an SSR app: a Vercel function fetches the built index.html, swaps
the marker-delimited social-meta block for repo-specific tags, and a
sibling function renders per-repo OG cards with @vercel/og (JetBrains
Mono TTFs; Satori can't consume WOFF2). Private repos and upstream
errors always get the generic site metadata plus noindex — repository
data is never interpolated on those paths. The client hook keeps
document meta in sync during SPA navigation, and the /api proxy narrows
to /api/v1 so local functions are reachable. Cache tiers: immutable
versioned OG URLs, 5m/1h SWR for pages, no-store on errors.

Author: kevincodex1

.gitignore

@@ -23,3 +23,4 @@ dist-ssr
 *.sln
 *.sw?
 .vercel
+.playwright-cli