feat(cli): cross-runtime start strategy (Node/Bun/Deno)

[SisyphusZheng]

Summary

Make the start CLI work across Deno, Node 18+, and Bun — or provide documented per-runtime alternatives. Currently cli/start.ts uses Deno.serve() and import.meta.main, making it Deno-only despite the project's cross-runtime claim.

Competitive context

Framework	Dev/Prod server runtime
SvelteKit	Node via adapters (node, cloudflare, vercel)
Next.js	Node (built-in server)
Astro	Node via adapters
Fresh	Deno-only (acceptable — Deno framework)
openElement	Deno-only start CLI (NOT acceptable — claims cross-runtime)

Proposed solution

Option A (preferred): Replace Deno.serve with node:http + Web Request/Response conversion:

• Works in Node 18+, Deno (node: compat), Bun
• ~40 lines of adapter code
• No external dependency

Option B: Generate a Nitro .output/ directory during build and delegate to node .output/server/index.mjs

Option C: Document start as Deno-only; add start:node and start:bun scripts

Related

• GitHub issue fix(cli): start command is Deno-only despite cross-runtime claim #622 (alpha.8 milestone) tracks the immediate fix
• This issue tracks the broader cross-runtime CLI strategy

Target version

0.43.0