Improve root onboarding and fix staged dev/check setup

[wesbillman]

Summary

• add a root README with quick start, command guide, repo layout, and troubleshooting
• improve root justfile UX with app discovery (just apps), friendly delegation errors, and aliases (just dev staged, just mark, just staged)
• make root checks fail-fast and add explicit just check (with just ci as an alias)
• fix staged dev port wiring so Vite honors VITE_PORT used by Tauri dev config
• add @types/node to apps/staged to satisfy its TypeScript node config
• ignore root .hermit and root node_modules/

Validation

• source ./bin/activate-hermit && just check
• pre-commit hook (fmt) passed during commit
• pre-push hook (ci) passed during push