Add og:type article + article:published_time

Every todo's PageMeta carries date, updated, and authors, but Meta.svelte:49 always sets og:type to website. None of the article-type signals are emitted, which is the largest gap between what the data model promises and what reaches crawlers.

Tasks

• Detect article-like pages (e.g. presence of date + authors) and set og:type=article
• Emit article:published_time from date (ISO via publicationDateToISO)
• Emit article:modified_time from updated when set
• Emit article:author for each author (resolve via the authors map)
• Optionally add a per-page meta name="author"