Resolves#37104
## Testing
- [X] Added/updated automated tests
- [X] Where appropriate, [automated tests simulate multiple hosts and
test for host
isolation](https://github.com/fleetdm/fleet/blob/main/docs/Contributing/reference/patterns-backend.md#unit-testing)
(updates to one hosts's records do not affect another)
- [ ] QA'd all new/changed functionality manually
<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit
* **New Features**
* Label validation now enforces team-context constraints for policies,
queries, and MDM profiles.
* Global policies now verify label validity before creation.
* **Bug Fixes**
* Improved label association verification in team-specific
configurations.
* **Tests**
* Added comprehensive test coverage for team label associations,
including label scoping validation and team deletion scenarios.
<sub>✏️ Tip: You can customize this high-level summary in your review
settings.</sub>
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
---------
Co-authored-by: Ian Littman <iansltx@gmail.com>
