Add Deno to the package-manager options

[bartlomieju]

👋 Bartek from the Deno team here.

This adds Deno as a fifth option to the package-manager widgets, alongside npm / yarn / pnpm / bun. Since the tabs are generated by your shared <Npm> / <Npx> / <NpxCompact> components, Deno now appears on every install/exec snippet across the docs, e.g. on the get-started pages:

deno add drizzle-orm pg dotenv

A few notes on the choices:

• Install uses deno add to match the surrounding yarn add / pnpm add / bun add style. Deno is a drop-in replacement for npm these days, so deno add drizzle-orm works the same way as the others (reads/writes package.json).
• Exec uses deno x (Deno's npx/bunx equivalent), e.g. deno x drizzle-kit generate.
• I kept the package-manager selector in sync, the packageManagers arrays in DocsLayout/CenteredLayout, so picking the Deno tab persists across widgets like the existing options do.
• Small robustness tweak: the inline <select> width-resizer now measures the selected option's text instead of the short package-manager name.

I verified locally with pnpm astro check (0 errors) and by checking the rendered tabs/commands on the get-started pages.

One thing worth flagging: the exec widget prefixes commands generically, so the "run your code" step renders deno x tsx src/index.ts. That works, though on Deno you can run TypeScript directly (deno run -A src/index.ts) without tsx. Happy to special-case that step if you'd prefer.

Totally fine to close this if you'd rather not add another tab. Happy to adjust anything.

Disclosure: I work on Deno, so I have an interest here. The goal is parity with the package managers you already list, not promotion. This PR was prepared with AI assistance under human supervision: I review every change myself and personally respond to any comments or review feedback.