feat: server rendering

[MohamedH1998]

What & why

What & why

This PR adds configurable request rendering for documentation and API collections while preserving existing static rendering behavior.

Request-rendered pages use the same resolution and projection paths as prerendered pages. Build-only work is prepared ahead of time so Workers do not require filesystem access, Git, native modules, OpenAPI parsing, or other build dependencies.

Key changes:

• Adds site-wide and per-collection build/request rendering policies.
• Supports mixed and fully request-rendered documentation sites.
• Preserves Markdown twins, navigation, API pages, last-updated dates, redirects, and 404 behavior.
• Includes request-rendered pages in sitemap, Pagefind, llms.txt, and OG discovery surfaces.
• Supports nested and parameterized reusable partials in request-rendered Markdown.
• Keeps API root, version, and leaf OG metadata aligned with generated assets.
• Updates the canonical starter source and registry guidance.
• Adds a workerd-based CI gate covering runtime behavior and bundle purity.

Reviewers should focus on static backward compatibility, collection/version resolution, build/runtime separation, and parity across discovery surfaces.

Validation completed:

• pnpm typecheck
• pnpm -r test
• pnpm templates:check
• pnpm workers-feasibility:check
• pnpm api-reference:check

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 because the starter changed)
• pnpm typecheck, pnpm -r test, and pnpm templates:check all green

[pkg-pr-new]

pnpm add https://pkg.pr.new/@cloudflare/create-nimbus-docs@104

pnpm add https://pkg.pr.new/@cloudflare/nimbus-docs@104

commit: 77b34b6