[codex] Add OGP metadata support

[nac-39]

Summary

• Adds default OGP and Twitter Card metadata using the production https://nac-39.com URL.
• Adds canonical URLs and per-page og:url values.
• Adds article-specific OGP metadata for title, description, image, URL, published time, and tags.
• Normalizes article date parsing and fixes generated blog paths so months are not zero-based.

Validation

• yarn build passed.
• yarn generate was attempted locally, but the current working tree includes untracked article files and image-heavy content that triggered Node heap OOM during IPX image generation. Those untracked article files are not included in this PR.