feat(release): @plumb npm org + @plumb/cli wrapper package

[aram-devdocs]

Summary

Publish @plumb/cli on npm as a thin wrapper that downloads
the right platform binary on install. Managed by cargo-dist's
npm installer feature.

Crate / area

release — release artifacts (cargo-dist, release-please, installers)

Phase / batch

Part of #49 → Batch 5A (Registries + tap infra).

Effort: M

PRD references

• PRD §15.1

Acceptance criteria

• npm i -g @plumb/cli installs on macOS / Linux / Windows.
• NPM_TOKEN configured as a repo secret.
• cargo-dist npm-scope field uncommented.

Dependencies

• None (first in batch; batch-level deps gate this).

Review gates

• 02-spec-reviewer
• 03-code-quality-reviewer
• 05-architecture-validator
• 04-test-runner
• 06-security-auditor

How to deliver

Dispatch /gh-issue <this-issue-number>. See the root AGENTS.md and the scoped release/AGENTS.md for the invariants that apply.

Suggested delivery: gh-issue

[aram-devdocs]

Evidence update from PR #200: #200

This change adds repo-owned validation and documentation proving the current non-manual release/install channel contract:

• bash tests/install-smoke-validate.sh passes
• bash tests/release-security-validate.sh passes
• bash tests/release-readiness-matrix-validate.sh passes
• git diff --check passes

What this PR does for #52:

• keeps npm explicitly gated/prep-only in install-smoke.yml, release.yml, dist-workspace.toml, and the v0 release-readiness runbook
• strengthens validator coverage so cargo and curl are the only active non-manual channels while npm remains gated
• updates stale readiness wording around chore(main): release 0.0.2 #101 without treating feat(release): @plumb npm org + @plumb/cli wrapper package #52 as complete

#52 remains open. This PR does not reserve or verify the @plumb scope/package, does not uncomment npm-scope, does not add NPM_TOKEN or publish permissions, and does not verify a live npm i -g @plumb/cli path.