docs: align health route and Nitro examples

[MisterJimson]

Summary

• update quickstart, init, and troubleshooting docs to use /health instead of /api/health
• change Nitro config examples to use "/**" so they match the junior init scaffold
• expand the handler surface reference to document the mixed root-level and /api route layout exposed by createApp()

This corrects the docs based on what I'm seeing in the code and experiencing in my deployed instance. Let me know if you would prefer the reverse fix and update the implementation to match current docs.

Test plan

• Run pnpm docs:check
• Confirm packages/junior/src/app.ts mounts /health
• Confirm packages/junior/src/cli/init.ts scaffolds "/**": { handler: "./server.ts" }

[vercel]

@MisterJimson is attempting to deploy a commit to the Sentry Team on Vercel.

A member of the Team first needs to authorize it.

[dcramer]

🙏 thanks!