[Epic] Add JSON output and release manifest generation

[phamhungptithcm]

Goal

Produce machine-readable output and release packets that are useful in CI, release review, and audits.

Scope

• JSON output contracts
• Markdown release manifest output
• report sections for risks, dependencies, and manual steps
• stable schema for future automation

Task Checklist

• define JSON output for scan, inspect, diff, and plan-style commands
• define Markdown release manifest structure for human review
• include explicit status fields such as safe, warning, manual-review, and blocked
• include risk, dependency, and repository-level evidence sections
• add contract tests for structured output

Acceptance Criteria

• CI and release pipelines can consume gig output without scraping terminal text
• reviewers can open one generated manifest and understand what is going into a release
• schema evolution is controlled and documented

References

• docs/03-cli-spec.md
• docs/10-error-handling-and-logging.md
• docs/18-operating-model.md