v4.0.0 — user-global install model

Breaking: DOX tooling now installs user-global. The agent-guided AGENT-INSTALL.md is the only install path (no install scripts) and never writes into a project — not even .gitignore.

• Skills and rule install once per user: ~/.agents/skills/ (Codex), ~/.claude/skills/ (Claude Code), ~/.gemini/config/skills/ (Antigravity), ~/.cline/skills/ (Cline); rule via global rules locations plus marker-guarded pointer blocks in ~/.codex/AGENTS.md / ~/.claude/CLAUDE.md.
• Project truth stays committed and is owned by the skills: the DOX.md tree and the root AGENTS.md/CLAUDE.md anchors (DOX shim) created or merged by dox-init / dox-upgrade. A fresh clone steers any agent to DOX.md with zero tooling installed.
• Cursor explicitly supported: discovers the shared global skill copies natively and reads AGENTS.md anchors root and nested — no separate install target.

Migration from v3 project-scoped installs: re-run the install prompt once per user; old gitignored project adapters and marker ignore blocks can be removed manually (with review).