feat(@angular/cli): add support for the nub package manager

[colinhacks]

PR Checklist

• The commit message follows our guidelines: https://github.com/angular/angular-cli/blob/main/CONTRIBUTING.md#-commit-message-guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• Other... Please describe:

What is the current behavior?

The CLI does not recognize nub as a package manager. It is rejected or silently defaulted to npm at every allowlist site: lockfile discovery ignores nub.lock, the schematics executor throws UnknownPackageManagerException, and the packageManager schema enums plus the npm create @angular user-agent allowlist exclude it.

Issue Number: N/A

What is the new behavior?

nub is recognized wherever the other package managers are. nub is pnpm-CLI-compatible and writes a pnpm-v9-format lockfile (nub.lock), so its handling mirrors pnpm throughout.

• packages/angular/cli/src/package-managers/package-manager-descriptor.ts — adds a nub descriptor to SUPPORTED_PACKAGE_MANAGERS, cloned from the pnpm descriptor with binary: 'nub' and lockfiles: ['nub.lock'], and adds nub to PACKAGE_MANAGER_PRECEDENCE. Lockfile discovery (discovery.ts) is data-driven off the descriptor's lockfiles, so nub.lock is now detected automatically — no separate change needed there.
• packages/angular_devkit/schematics/tasks/package-manager/executor.ts — adds a nub entry to the executor map (installAll: 'install', installPackage: 'add'), which previously threw UnknownPackageManagerException.
• packageManager schema enums — adds "nub" to packages/schematics/angular/ng-new/schema.json, packages/schematics/angular/workspace/schema.json, packages/angular/cli/lib/config/workspace-schema.json (both occurrences), and packages/angular_devkit/schematics_cli/{schematic,blank}/schema.json.
• packages/angular/create/src/index.ts — adds 'nub' to the user-agent allowlist in the npm create @angular shim. nub's user agent is nub/<ver> …, which the shim parses as nub via split('/')[0].

Does this PR introduce a breaking change?

• Yes
• No

Other information

The nub descriptor mirrors pnpm because nub implements the pnpm CLI grammar and lockfile format; no nub-specific parsing was required. A signed Google CLA is still pending on my side.

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.

[gemini-code-assist]

Code Review

This pull request adds support for a new package manager named nub across the Angular CLI and schematics. The changes include updating various workspace and schematic schemas to include nub in the packageManager enum, defining its descriptor and precedence in the package manager configurations, and adding its execution commands. There are no review comments, so I have no feedback to provide.