…3813)

* Validate stale Agent release requirements

* Skip unreleased integrations in Agent release output

* Tighten unreleased-integrations parsing and broaden tests

- Validate that by-agent-version-range keys contain the '..' separator and raise a clear ValueError naming the offending key.
- Drop the redundant else branch in exclude_unreleased_integrations and move the historical folder-name comment back next to normalize_catalog.
- mkdir(exist_ok=True) in the write_repo_config helper for consistency with neighbours.
- Parametrize test_agent_version_in_range_is_inclusive (now covers below/above bounds and the malformed-range error path).
- Add a direct unit test on get_unreleased_integrations that exercises by-integration and by-agent-version-range together.
- Add a clean-pass test for validate agent-reqs and pull the set_root teardown into an isolated_root yield fixture.
- Add changelog entries for ddev and datadog_checks_dev.

* Surface malformed version ranges as a clean ddev abort

- Drop the redundant empty parent table header in .ddev/config.toml; the two sub-tables imply it.
- Catch ValueError from agent_version_in_range at every command entry point that triggers the lookup (integrations, changelog, integrations_changelog) and surface it via app.abort so config authors get a clean message instead of a Python traceback.
- Document that exclude_unreleased_integrations accepts both raw and folder-normalized catalog keys.

* Scope stale-entry detection to whole-file invocations

When the user runs `ddev validate agent-reqs <check>`, only the requested check should be validated; previously the new stale-entry detection still scanned the whole requirements file and surfaced unrelated stale packages, defeating per-check pre-commit usage.