Externalize provider Agent Host ownership

[rudijetson]

Summary

• Make vendor-installed Codex, Claude, Gemini, and Antigravity CLIs the only Agent Host execution sources.
• Keep RUDI Node and Python ownership for tools, MCP stacks, and daemon infrastructure.
• Reject Agent Host package installation and update paths and remove installed-agent fallback metadata.
• Make legacy cleanup provenance-safe and preserve unknown user wrappers.
• Strip RUDI-owned and relative PATH entries from provider child processes.
• Add ADR, migration and rollback notes, and explicit status, check, and list semantics.
• Release as CLI 1.10.20 with a dedicated generated bundle commit.

Verification

• pnpm test: 661 passed
• pnpm build
• configured RUDI debt scan: 0 findings
• repository debt runner: 0 findings
• npm pack --dry-run --json
• deterministic rebuild hashes: stable
• git diff --check
• independent release review: READY

Coordinated with the Registry Agent Hosts 0.1.2 and Registry 2.0.1 PR from the same branch name.

Supersedes the partial ownership and preflight work in #14 and #25.