docs: surface Bun runtime on the marketing website and README quickstart

[vivek7405]

Problem

First-class Bun runtime support (#508, #541) is a headline capability surfaced prominently on the docs site and in the README, but the marketing website never mentions it. A grep for bun across website/** (excluding "bundle") returns nothing: the landing copy, feature cards, and the DESCRIPTION meta in website/app/layout.ts only say "no-build / Node-class". The website is the lone surface that omits a headline feature.

Separately, the README quickstart block (the most-copied snippet, around L52 to L66) shows only npm create webjs@latest and never the Bun path (bun create webjs my-app or --runtime bun), even though the README headline and feature list do mention Bun.

Implementation notes (for the implementing agent)

• Where to edit:
  • website/app/page.ts: add a Bun mention to a feature card or the hero.
  • website/app/layout.ts: include Bun in the DESCRIPTION meta.
  • README.md (quickstart block around L52 to L66): show the Bun scaffold path alongside the npm one.
• Source of truth: Support both Bun and Node runtimes (first-class create + run) #508 / Add a Bun-first scaffold mode (--runtime bun) across all 3 templates #541 (Bun is first-class for create and run; bun create webjs, bun --bun run dev / start, --runtime bun across all three templates). The docs getting-started page already shows the Bun scaffold commands; mirror them.
• Landmine: the website is dogfooded and Tailwind-first; match the existing component / copy style and respect the prose-punctuation invariant. Do not hand-write the changelog (it is auto-generated).

Acceptance criteria

• The marketing website surfaces Bun as a supported first-class runtime (a feature card or hero plus the meta description).
• The README quickstart shows the Bun scaffold path.