feat(create-astro): add nub package manager support

[colinhacks]

Changes

create-astro already detects nub as the active package manager (from npm_config_user_agent) and drives it correctly for install and astro add via the generic passthrough and nub dlx. Two printed run commands were still wrong for nub:

• next-steps.ts — the commandMap had no nub entry, so nub users fell back to npm run dev. Added nub: 'nub run dev'.
• template.ts (processTemplateReadme) — the non-npm path replaced npm run with the bare package-manager name, turning npm run dev into nub dev. nub has no implicit script shortcut, so that is invalid. It now maps npm run <script> to nub run <script>, keeping the explicit run.

pnpm/yarn/bun output is unchanged. Changeset included.

Testing

Verified the code path a nub user hits: detection yields packageManager === 'nub', commandMap.nub returns nub run dev, and processTemplateReadme rewrites npm run dev to nub run dev while leaving bare npm (e.g. npm install -> nub install) and the pnpm/yarn/bun branches untouched.

Docs

No docs change needed — this only corrects the package-manager commands create-astro prints for an already-detected manager.

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[changeset-bot]

🦋 Changeset detected

Latest commit: c8dc949

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
create-astro	Patch

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