Part of #430.

Tasks

• Rework website/ top-level structure: "Convention" (frontmatter + config), "Linter", "Skills", "Recommended stack" (Obsidian plugin, VS Code tips)
• "Migration from v-last-webapp" guide walking users through the migration CLI
• Landing page pitch: "Architecture docs for the age of coding agents — bring your own editor"
• Update root CLAUDE.md: remove web-app notes; describe new package layout and the new sync rule (schema fields must stay in sync across @scope42/data, @scope42/lint, skills templates, and plugin templates)