gokaygul.com OG image service

Endpoints:
  GET  /horizontal?title=...&subtitle=...&category=...&theme=dark|light  → 1200×630
  GET  /square?title=...&subtitle=...&slide_no=1&theme=dark|light       → 1080×1080
  GET  /vertical?title=...&subtitle=...&cta_url=...&theme=dark|light    → 1080×1920
  POST /parse-frontmatter  body { path, content_base64 }  → JSON