Add content-as-code news system

We added a news system to getpeppr, powered by Markdown files with typed frontmatter.

What's new

• Console — A new "Changelog" page in the sidebar shows product updates in a dense, developer-friendly format
• Website — A public /news section displays all announcements and changelogs with cards, type badges, and tags
• Content package — A shared @getpeppr/content package parses and validates Markdown news entries with Zod

All content lives in packages/content/news/ — just add a .md file and push to publish.