feat: zero new --json envelope

[mkitsugi]

zero new is the only project-scaffolding entry point without a JSON envelope. Adds --json with kind, name, path, manifest, entry, and nextSteps so scaffold output can be consumed structurally.

$ bin/zero new --json cli mycli
{
  "schemaVersion": 1,
  "ok": true,
  "kind": "cli",
  "name": "mycli",
  "path": "mycli",
  "manifest": "mycli/zero.json",
  "entry": "mycli/src/main.0",
  "nextSteps": ["zero check mycli", "zero test mycli", "zero run mycli"]
}

Plain-text output is unchanged. lib omits zero run in nextSteps. The new arg parser is rewritten to be order-independent so --json can appear before or after the positional args.

[vercel]

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