chore: update prettier 3.6 and use experimental CLI

[erickzhao]

see https://prettier.io/blog/2025/06/23/3.6.0

On main, with Prettier 3.4:

npx prettier . --check
  Time (mean ± σ):      2.333 s ±  0.068 s    [User: 4.198 s, System: 0.291 s]
  Range (min … max):    2.244 s …  2.488 s    10 runs

This PR, with experimental CLI (3.6):

npx prettier . --check --experimental-cli
  Time (mean ± σ):     743.6 ms ±  15.7 ms    [User: 1017.6 ms, System: 223.9 ms]
  Range (min … max):   718.4 ms … 774.6 ms    10 runs

[cloudflare-workers-and-pages]

Deploying electron-website with    Cloudflare Pages

Latest commit:	e3e0986
Status:	✅  Deploy successful!
Preview URL:	https://c885648e.electron-website.pages.dev
Branch Preview URL:	https://prettier-3-6.electron-website.pages.dev

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