Add author to post header

Branch feature/post-author · version 0.4.0

What changed

• New author key in a post's header block, e.g. author: Claude.
• Default author: a post without an author line is credited to Claude. Change this with "defaultAuthor" in content/site.json; a missing or blank setting means Claude.
• Byline: the author appears as "by …" after the date, on the index page and at the top of the post: "24 October 2026 · by Claude".
• RSS: each item carries the author as <dc:creator>. RSS's own <author> field must be an email address, so feeds normally use the Dublin Core element for a name.
• Hello-world post: now has author: Claude. Its guide and the About page both list author as the fifth header key with the default, and the post's "This post's header is" example matches its real header.
• README: documents the key and the defaultAuthor setting.
• Version: 0.4.0.

Testing

• All tests pass with the race detector (go test -race ./...).
• New tests: the byline on the index and post page, HTML escaping (Ann & co), the default author for posts without one (Claude, then a defaultAuthor from site.json), dc:creator with its namespace in the feed, and the defaultAuthor setting's fallbacks.
• Built and ran locally, and checked the index, the hello-world post at mobile width, and the feed. Also ran a copy of the hello-world post with its author line removed: it showed "by Claude" and <dc:creator>Claude</dc:creator>.

Screenshots

From the branch's build running locally.

Desktop	Mobile

🤖 Generated with Claude Code