chore(n): add setup-repos to clone + build managed plugins

[adekbadek]

All Submissions:

• Have you followed the Newspack Contributing guidelines?
• Does your code follow the WordPress coding standards and VIP Go coding standards?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

Changes proposed in this Pull Request:

Adds a thin bootstrapper so a fresh checkout can pull in the two plugins that can't live in this monorepo because they're in separate private repos: newspack-manager and newspack-manager-admin. Previously these had to be cloned by hand, with no convention.

n setup-repos clones both into repos/plugins/ via the GitHub CLI (so its auth covers the private repos), skipping any that are already present, then builds each through the existing standalone-repo path (the same one n build <name> uses) and symlinks them into the running site via link-repos.sh. They show up in the plugins list ready to activate, no restart needed. Pass --env <name> to build and link into an isolated environment instead of the main site.

This builds on the existing repos/{plugins,themes} convention, the ./repos:/newspack-repos mount, and link-repos.sh symlinking (#177/#178). It also adds the ./repos mount to the isolated-env compose template, which was the one place that mount was missing, so the repos/ convention now works in isolated envs too.

How to test the changes in this Pull Request:

1. Ensure the GitHub CLI is authenticated for the private Automattic repos (gh auth status).
2. From the workspace root, run n start and n install (or use an existing running site).
3. Run n setup-repos. Confirm it clones newspack-manager and newspack-manager-admin into repos/plugins/, builds each, and symlinks both into wp-content/plugins/.
4. In wp-admin (or via wp plugin list), confirm both plugins appear and activate with no fatals (with newspack-plugin active). Confirm the homepage still loads.
5. Run n setup-repos again and confirm it reports both as already present and skips the clone (idempotent).
6. Isolated env: n env create managed-test --up, then n setup-repos --env managed-test. Confirm the env container mounts /newspack-repos, both plugins symlink into the env's wp-content/plugins/, and activate with no fatals. Tear down with n env destroy managed-test.
7. Run n setup-repos without gh installed/authenticated and confirm it fails fast with a clear error before attempting any build.

Other information:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes, as applicable?
• Have you successfully run tests with your changes locally?

[Copilot]

Pull request overview

Adds an n setup-repos bootstrap command to standardize cloning and wiring up the two private “managed” plugins (newspack-manager, newspack-manager-admin) into the workspace repos/plugins/ convention, including isolated env support.

Changes:

• Add n setup-repos [--env <name>] to clone managed plugins on the host (via gh), then build + symlink them inside the target container.
• Introduce bin/setup-repos.sh and a managed_plugins list in bin/repos.sh to drive the bootstrap flow.
• Mount ./repos into isolated env containers (/newspack-repos) and document the workflow in AGENTS.md.

Reviewed changes

Copilot reviewed 2 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
n	Adds setup-repos command wiring (clone on host, build/link in container) and updates help output.
bin/setup-repos.sh	New host-side script to clone the private managed plugin repos into repos/plugins/.
bin/repos.sh	Adds a managed_plugins array used by n setup-repos/setup-repos.sh.
bin/env.sh	Adds the ./repos:/newspack-repos mount to isolated environment compose generation.
AGENTS.md	Documents n setup-repos in first-time setup and the repos/ convention.