fix(cli): honour -f json on the error envelope

[ankitranjan7]

webcmd … -f json still printed YAML error envelopes. An agent that JSON.parses stderr died on every built-in or adapter failure.

After

$ webcmd validate nope -f json
# stderr, exit 2
{
  "ok": false,
  "error": {
    "code": "ARGUMENT",
    "message": "No command matches \"nope\". …",
    "exitCode": 2
  }
}

• -f json → JSON envelope on stderr
• every other format, and no -f, → existing YAML envelope
• AutoFix # comments are YAML-only so JSON stays parseable
• Same path for local built-ins (reportCliError), adapter commands, and hosted typed errors

Hosted impact

Hosted impact: B — rides the pin bump
Trigger: none
Why: CLI presentation only (`formatErrorEnvelope`). Cloud already returns JSON `{ok:false,error}` over HTTP; no cloud code or contract change.
Sequencing: none. Behaviour reaches hosted CLI users at the next bump:webcmd.

Verification

• npx tsc --noEmit — clean
• npx vitest run --project unit src/output.test.ts src/cli-error-report.test.ts src/commanderAdapter.test.ts src/hosted/runner.test.ts — 180 passed

[github-actions]

🟠 Maintainer review suggested — low confidence

The automated review could not reach a fully supported conclusion.

This review is advisory and does not block merging.