[feature]: Structured gate verdicts via JSON schema

[faisalishfaq2005]

What problem would this solve?

Gates today emit plain-text VERDICT: PASS/FAIL, parsed by regex in src/core/verdict.ts. There's no way for a gate to return structured findings (severity, file, line) that tooling could act on. This is a roadmap item.

Proposed solution

Allow a step to optionally declare an expected JSON shape so a gate can return structured output, while keeping the plain-text protocol as the default. Needs a design proposal first — please discuss the protocol in the Ideas discussion before implementing.

Alternatives considered

No response

Scope

• I've checked this isn't already on the roadmap in the README.
• This can't reasonably be expressed as a loop instead of engine code.