feat: add safe CLI script uninstallers

[bbednarski9]

Overview

Add supported, safety-first uninstall scripts for NeMo Relay CLI binaries installed with install.sh or install.ps1. The scripts provide a clean reinstall path without removing Relay configuration, output, PATH entries, or coding-agent integrations.

• I confirm this contribution is my own work, or I have the right to submit it under this project's license.
• I searched existing issues and open pull requests, and this does not duplicate existing work.

Details

• Add root-level Unix shell and PowerShell uninstallers with matching default install locations, custom install-directory support, dry-run support, idempotent absent-install handling, and explicit help text.
• Limit removal to the selected installed nemo-relay binary. Preserve its installation directory, PATH changes, Relay configuration and observability output, and managed coding-agent integrations.
• Refuse a normal uninstall while the selected binary has active Relay processes.
• Keep force mode interactive and prompt once per detected shutdown tree:
  • For an MCP Relay process, select a recognized Codex, Claude, or pi ancestor when one can be established.
  • If no coding-agent owner can be established, target only the Relay MCP process instead of guessing that an adjacent shell, plugin host, or supervisor owns it.
  • Deduplicate multiple MCP processes owned by the same coding-agent process.
• Refuse force shutdown when the proposed target is an ancestor of the uninstaller itself. This prevents the script from killing its own shell before binary removal and directs the user to rerun from an independent terminal.
• Verify the installed executable's identity, including binaries launched through PATH or by absolute path. Immediately before signaling, revalidate the target relationship and stable process identity (parent/start time on Unix; parent/creation time/executable path on Windows) to avoid PID-reuse races.
• Treat an exited-but-unreaped Unix zombie as stopped so binary removal does not wait on a parent process to reap it.
• Emit PowerShell process diagnostics directly to stderr so $ErrorActionPreference = 'Stop' does not bypass dry-run or force-confirmation control flow.
• Keep process safety in the standalone uninstallers so a current script can remove an older script-installed CLI that does not provide a newer package-uninstall command.
• Document default and custom-directory uninstall, package-manager alternatives, optional integration cleanup, and the download-first PowerShell invocation required for -Force or -InstallDir.
• Add the uninstallers and their tests to the existing installer CI path filter and Linux, macOS, and Windows matrix.

The change is not breaking. Existing CLI-managed integrations remain installed unless the user explicitly runs nemo-relay uninstall all before removing the binary.

Validation:

• sh scripts/test-install.sh
• sh scripts/test-install-mocks.sh
• sh scripts/test-uninstall.sh — 8 groups, including active-process refusal, accepted/rejected force confirmation, process-tree termination, MCP-owner deduplication, absolute-path discovery, and self-tree refusal
• pwsh -NoProfile -NonInteractive -ExecutionPolicy Bypass -File scripts/test-uninstall.ps1
• PowerShell parser validation
• YAML parsing and git diff --check
• GitHub Check / Run passed, including repository pre-commit checks
• Installer matrix passed on Linux x86-64/ARM64, macOS ARM64, and Windows x86-64/ARM64
• Fern content validation passed; the current preview publication failure is in the remote ledger's theme-asset upload step
• The current Windows ARM Go failure is an unrelated existing clang -mthreads toolchain issue

Where should the reviewer start?

Start with the shutdown policy in uninstall.sh and uninstall.ps1, especially MCP-owner resolution, self-tree refusal, and process-identity revalidation. Then review scripts/test-uninstall.sh for the destructive process-tree scenarios and scripts/test-uninstall.ps1 for Windows active-process, dry-run, and confirmation coverage.

Related Issues: (use one of the action keywords Closes / Fixes / Resolves / Relates to)

• Relates to [Bug]: a dangling Codex marketplace registration breaks install, uninstall, and refresh #968. That issue covers recovery from dangling Codex marketplace registrations; this PR only removes the script-installed CLI binary and intentionally leaves integrations untouched.

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Fern docs preview: https://nvidia-preview-pull-request-1008.docs.buildwithfern.com/nemo/relay/dev