registry: use aqua backend for npm

[risu729]

Summary

• Reopens registry: use aqua backend for npm #8185 with only the registry/npm.toml change.
• Prefer aqua:npm/cli while keeping npm:npm as the fallback backend.
• Add the node dependency required to run the npm JavaScript entrypoint.
• Keep the registry test as npm --version; it should not check node --version.
• Update the backend-arg unit test now that bare npm resolves through the registry to aqua:npm/cli.
• Keep explicit coverage for npm:npm as the npm backend form.
• Clarify why the npm backend still waits for node when bootstrapping npm:npm.

Notes

• The aqua registry entry has not merged yet: feat: add npm/cli aquaproj/aqua-registry#48803
• This relies on recent mise aqua file-link / hard: true support from fix(aqua): support registry file links #9610

Testing

• cargo test test_bare_
• cargo test test_get_dependencies_for_npm_itself
• cargo fmt --check
• git diff --check

[gemini-code-assist]

Code Review

This pull request updates the npm registry configuration to prioritize the aqua:npm/cli backend. It includes a clarifying comment in the NPM backend implementation regarding bootstrapping and updates the CLI argument parsing tests to ensure that a bare 'npm' input correctly resolves to the Aqua backend. I have no feedback to provide as there were no review comments.

[greptile-apps]

Greptile Summary

This PR updates the mise registry so that bare npm prefers the aqua:npm/cli backend while keeping npm:npm as the fallback, matching the pattern used by other tools that have graduated to the aqua backend.

• registry/npm.toml: adds aqua:npm/cli as the first-choice backend; npm:npm is retained so the fallback path is intact until the upstream aqua-registry PR (#48803) merges.
• src/backend/npm.rs: replaces a stale comment with a clear explanation of why node remains a dependency when bootstrapping through the npm:npm path even after the registry shorthand moves to aqua.
• src/cli/args/backend_arg.rs: splits the old bare-npm test into an explicit npm:npm case and a new async registry-resolution test asserting bare npm resolves to aqua:npm/cli.

Confidence Score: 5/5

Safe to merge — the change is additive (aqua backend is preferred, npm:npm fallback is preserved) and the only runtime behaviour change is when the aqua-registry entry for npm/cli eventually lands.

The registry change is minimal and non-breaking: existing npm:npm users are unaffected, bare-npm users will seamlessly fall back until the upstream aqua PR merges, and the updated tests correctly cover both the explicit and registry-resolved code paths.

No files require special attention.

Important Files Changed

Filename	Overview
registry/npm.toml	Adds aqua:npm/cli as the preferred backend with npm:npm kept as the fallback; the rest of the file is unchanged.
src/backend/npm.rs	Comment-only change that clarifies why node is kept as a dependency for the npm:npm bootstrap path even after the registry shorthand moves to aqua.
src/cli/args/backend_arg.rs	Splits the old bare-npm test into two: an explicit npm:npm test and a new async test verifying bare npm resolves through the registry to aqua:npm/cli.

_{Reviews (2): Last reviewed commit: "Merge branch 'main' into test/npm-aqua-f..." | Re-trigger Greptile}