claude-code: reach one-command install and clean uninstall parity

[SignalLayerLabs]

Context

MARGINAL already supports Claude Code in Observe mode.

The goal is to bring the installation and removal experience up to the standard of the current Codex integration.

Target UX:

install MARGINAL
→ enable Claude Code integration
→ open Claude Code
→ MARGINAL works

Contribution wanted

Implement the complete Claude Code installation and removal path.

Acceptance criteria

• One documented command installs/enables MARGINAL for Claude Code.
• Re-running installation is idempotent.
• Existing unrelated Claude Code configuration is preserved.
• Installation verifies that the expected MARGINAL hooks/plugin are actually available.
• Partial installation failures fail safely and do not break Claude Code.
• Uninstall removes only MARGINAL-owned files or configuration.
• Clean uninstall leaves Claude Code operational.
• No manual configuration editing unless Claude Code itself makes it unavoidable.
• Exact tested Claude Code version(s) are documented.
• Automated tests cover install, reinstall, partial failure and uninstall.
• Existing Codex, OpenCode and PrivacyCode integrations remain unchanged.

Privacy

Installation and diagnostics must not persist prompts, source code, tool output, credentials or private paths.

Non-goal

This issue does not promote Claude Code beyond Observe.