Problem\nPost-IssueComment.ps1 can fail with HTTP 403 Resource not accessible by integration when posting an issue comment. This blocks tooling that relies on comments for follow-ups or corrections.\n\n## Observed behavior\n- Posting to repos/OWNER/REPO/issues/ISSUE/comments returns 403.\n- Issue creation may still succeed in the same environment.\n\n## Request\nImprove diagnostics and fallback behavior:\n- Detect 403 and output a clear explanation of likely causes (token type, GitHub App vs user token permissions).\n- Provide an alternative action when comments are not permitted (example: write the intended payload to a local artifact for manual posting, or fail with a structured error).\n\n## Acceptance criteria\n- 403 failures are reported with actionable guidance and a structured error payload.