chore: remove obsolete design tooling

[mastro993]

Summary

Remove obsolete design tooling and all repository wiring.

Changes

• Delete checked-in skill bundle, compatibility link, frontend sidecars, and GitHub hook.
• Remove Codex, Claude Code, and Cursor hook registrations.
• Remove lockfile, ignore rules, product marker, and provenance references.
• Preserve shared lifecycle hooks and apps/frontend/DESIGN.md.

How to test

1. pnpm check:frontend

Checklist

• pnpm check passes locally
• Relevant tests pass (pnpm check:frontend)
• Privacy reviewed — no real financial data, credentials, secrets, or unredacted logs in code, fixtures, or attachments
• Documentation updated when behavior, setup, or commands change
• Database migrations documented when schema changes affect existing local data
• UI screenshots or recordings attached when the change is visual