Part of #430.

Framed as optional. Obsidian is one supported editor; users may use VS Code, plain Git, or anything else.

Tasks

• Scaffold packages/scope42-obsidian using the official Obsidian sample plugin template
• Plugin reads scope42.yaml from the vault root to locate item folders (falls back to a friendly warning if missing)
• Reuse @scope42/data for parsing & validation; surface validation errors as in-editor notices
• Commands: "New {type}" (one command per configured type) that creates a correctly-named file with templated frontmatter stub and H1
• Auto-maintain created / modified timestamps
• Sidebar view: filtered tables by type with status & tag filters
• Status badges in the file explorer via CSS classes based on frontmatter status
• Inline warnings on unresolved relation IDs in frontmatter
• Document that native Obsidian graph / backlinks / search cover the UX of the old web app
• README with screenshots and install steps; plan a follow-up sub-issue for community-plugin submission