<!-- Add the related story/sub-task/bug number, like Resolves#123, or
remove if NA -->
**Related issue:** Resolves#37806
This PR creates an activity bounded context and moves the following HTTP
endpoint (including the full vertical slice) there:
`/api/latest/fleet/activities`
NONE of the other activity functionality is moved! This is an
incremental approach starting with just 1 API/service endpoint.
A significant part of this PR is tests. This feature is now receiving
significantly more unit/integration test coverage than before.
Also, this PR does not remove the `ListActivities` datastore method in
the legacy code. That will be done in the follow up PR (part 2 of 2).
This refactoring effort also uncovered an activity/user authorization
issue: https://fleetdm.slack.com/archives/C02A8BRABB5/p1768582236611479
# Checklist for submitter
If some of the following don't apply, delete the relevant line.
- [x] Changes file added for user-visible changes in `changes/`,
`orbit/changes/` or `ee/fleetd-chrome/changes`.
## Testing
- [x] Added/updated automated tests
- [x] QA'd all new/changed functionality manually
<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit
## Release Notes
* **New Features**
* Activity listing API now available with query filtering, date-range
filtering, and type-based filtering
* Pagination support for activity results with cursor-based and
offset-based options
* Configurable sorting by creation date or activity ID in ascending or
descending order
* Automatic enrichment of activity records with actor user details
(name, email, avatar)
* Role-based access controls applied to activity visibility based on
user permissions
<sub>✏️ Tip: You can customize this high-level summary in your review
settings.</sub>
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
