fix: rewrite OG templates as React elements — bypass HTMLRewriter

workers-og's parseHtml uses HTMLRewriter which corrupts HTML→VDOM
conversion on CF Workers (text chunking, phantom child nodes).
Passing React element objects directly to ImageResponse bypasses
parseHtml entirely and works reliably.

Rewrote all 4 OG endpoints to use React element builders:
- buildOgElement() for blog/podcast/course (logo, badge, title, author)
- buildDefaultOgElement() for generic pages (logo, title, URL)

All endpoints use arrayBuffer() pattern to catch stream errors.

Build: 21.75s ✅

Author: Miriad