artifact: add PR body generator example

[ProfRandom92]

Adds a deterministic Markdown example artifact for the PR body generator.

Validation:

• python -m compileall -q scripts/pr_body_from_agent_bundle.py scripts/generate_pr_body_from_agent_bundle_example.py
• pytest tests/test_pr_body_from_agent_bundle.py -q

[gemini-code-assist]

Code Review

This pull request introduces a deterministic PR body Markdown example along with a generation script and a regression test to ensure the committed artifact remains in sync with the generator. A review comment correctly identified that the artifact path in the test file is relative, which could lead to environment-dependent failures; a code suggestion was provided to anchor the path to the repository root for better robustness.

[gemini-code-assist]

The path PR_BODY_ARTIFACT_PATH is defined as a relative path. This makes the test environment-dependent and likely to fail if executed from a directory other than the repository root (e.g., from within the tests/ directory). It is recommended to anchor this path using the repository root. Since scripts.pr_body_from_agent_bundle (imported as pr_body) already calculates and exposes REPO_ROOT, you can use it here for consistency and robustness.

Suggested change

	PR_BODY_ARTIFACT_PATH = Path("artifacts/pr_body_from_agent_bundle_example.md")
	PR_BODY_ARTIFACT_PATH = pr_body.REPO_ROOT / "artifacts" / "pr_body_from_agent_bundle_example.md"