perf: hashless prerender bundles

[MohamedH1998]

What & why

Skip hashing Astro's temporary prerender bundle - shout out @ttmx for this

Speeds up large docs builds by giving Astro's throwaway prerender bundle
hashless filenames, so Rolldown skips its per-chunk hash-graph walk.

Why

Astro imports the prerender bundle to render static pages, then deletes it. On
large sites, hashing its thousands of lazy content chunks dominates the build —
Rolldown re-walks the transitive chunk graph once per hash placeholder, which is
wasted work on an intermediate that's thrown away.

Cloudflare Docs (~8.7k pages), isolated cold-build A/B:

	Wall time	Prerender bundling
Before (hashed)	7:44	3:51
After (hashless)	5:24	1:39

~30% less wall time, ~57% less prerender bundling.

What

• Hashless entry/chunk names for the prerender environment only — shipped
  client and asset hashes are unchanged.
• Writes Astro 7's native rolldownOptions output key, not the
  deprecation-track rollupOptions alias.
• Stays out of the way

Checklist

• A maintainer approved this work (lgtm+ on my issue or discussion), or I'm on the team
• Correct tier (framework / starter / registry) per the boundary test
• Edited packages/nimbus-starter-source/, not the templates branch
• Changeset added (create-nimbus-docs changeset if the starter changed)
• pnpm typecheck, pnpm -r test, and pnpm templates:check all green

First time here?

Nimbus works from issues and discussions, not drive-by PRs, so unapproved PRs from
outside the team are closed automatically. If that's you, open an
issue (bug or fix proposal)
or a discussion (feature) instead —
once a maintainer approves you there, your PRs stay open. See
CONTRIBUTING.md.

[pkg-pr-new]

pnpm add https://pkg.pr.new/@cloudflare/create-nimbus-docs@57

pnpm add https://pkg.pr.new/@cloudflare/nimbus-docs@57

commit: 5149194

[MohamedH1998]

Ran a cold A/B on the Cloudflare Docs build to check the real-world win
vite 8.1.5 / rolldown 1.1.5, 8,710 pages, 20,786 prerender chunks. Same
package, only the prerender hashing toggled:

	Prerender bundle phase	Total
Hashed (baseline)	1m53s	212s
Hashless (this PR)	1m50s	222s

The override works as intended — prerender chunks come back hashless — but it
saves ~3s here, within noise. For reference, even the hashed bundle phase is
1m53s, vs the 3m51s in the original measurement.

Looks like Rolldown has since sped up its chunk hashing, so the bottleneck this
targets is largely gone on the current stack. The change itself is correct and
safe — there's just no measurable build-time win anymore 😔.

Draft PR in the Cloudflare docs: cloudflare/cloudflare-docs#32304