docs: add final output receipt guidance

[aDragon0707]

Summary

Adds docs-only safety guidance for auditing final output claims in Claude Code Action workflows.

The section clarifies that Claude's final response is not proof that every completion claim is supported. It shows a compact receipt pattern that separates:

• completion claims
• supporting evidence
• unsupported or unverified claims
• next owner
• human approval boundaries

Motivation

Claude Code Action can review pull requests, triage issues, inspect CI failures, and prepare code changes.

Those final outputs may contain operational claims such as task completed, CI failure diagnosed, changes prepared, or ready for review. These claims can require evidence from changed files, command output, CI logs, GitHub comments, or human approval.

A compact receipt complements existing security controls by summarizing the final work state for humans and downstream workflow steps.

Notes

• Docs-only change.
• No runtime dependency.
• No behavior change.
• Safety-oriented guidance for final output review.

Verification

• git diff --check
• Not run: bun test / bun run format:check because bun is not installed in this local environment.