Add the devlog section

Added a /devlog section for logging chunks of work — a markdown file per entry in content/devlog/, parsed the same way as recipes and roadtrips, but with a freeform Markdown body instead of a custom ingredients/directions DSL.

What changed

• New lib/devlog.ts parser (title, start/end date, description, tags)
• Listing page at /devlog, sorted newest-first
• Entry pages at /devlog/[slug], body rendered via react-markdown + remark-gfm
• Linked from /dashboard

Notes

Tables, inline code, and bold/italic all render through the shared Tailwind typography styles.