Add host_id and host_serial to Apple mdm_enrolled activity (#49969)

<!-- Add the related story/sub-task/bug number, like Resolves #123, or
remove if NA -->
**Related issue:** Resolves #49777

## Description

Adds `host_id` and `host_serial` to the Apple `mdm_enrolled` activity so
IT admins can build automations on top of it, and surfaces the activity
on the individual host's activity timeline.

- **`server/fleet/activities.go`** — added `HostID` to
`ActivityTypeMDMEnrolled` and a `HostIDs()` method (mirrors the existing
`ActivityTypeMDMUnenrolled` pattern), so the activity is linked to the
host and appears on its timeline.
- **`server/mdm/lifecycle/lifecycle.go`** — populate `host_id` for
macOS/iOS/iPadOS enrollments. Account-driven user (BYOD) enrollments
have no hardware serial, so they report the enrollment ID as
`host_serial` too, keeping `host_serial` populated for automations
regardless of enrollment type.
- **Frontend** — new `MdmEnrolledActivityItem` component, registered in
the host past-activity component map (and the `IHostPastActivityType`
union), renders the now-host-linked `mdm_enrolled` activity on the host
details **Activity** card. There's no Figma, so the copy mirrors the
sibling `mdm_unenrolled` item (e.g. "Mobile device management (MDM) was
turned on for this host").

`host_id` uses `omitempty`, so Windows (`microsoft_mdm.go`) enrollments
keep their existing activity payload unchanged — Windows is
intentionally out of scope, handled in #47874, which also owns the
audit-log documentation update for the shared field.

> **For reviewer:** the ADUE `host_serial = enrollment_id` behavior
comes from the issue's test plan. It means `host_serial` and
`enrollment_id` carry the same value for BYOD. Flagging in case Product
would rather leave `host_serial` empty for ADUE and have automations
read `enrollment_id`.

## Testing

- **Automated:** `TestMDMEnrolledActivityHostIDAndSerial`
(`server/mdm/lifecycle`) covers device enrollment (`host_serial` =
hardware serial) and ADUE (`host_serial` = enrollment ID), both
asserting `host_id`/`HostIDs()`. Also verified `server/datastore/mysql`
`TestMDMEnrollment`, `server/activity/internal/mysql`
`TestListActivities`, and `server/service` `TestMDMTokenUpdate*` pass.
- **Live (simulated) manual macOS enrollment** via `osquery-perf`: the
`mdm_enrolled` activity recorded `host_id` + `host_serial`, and an
`activity_host_past` row linked it to the host (confirmed it shows on
the host timeline).
- **Frontend:** `MdmEnrolledActivityItem.tests.tsx` covers the rendered
copy for macOS/iOS/Android and the actor/no-actor variants; also
visually confirmed the activity renders on a host's Activity card in the
running app. `yarn jest`, `eslint`, and `tsc` pass.
- Updated the MDM integration tests (`integration_mdm_test.go`,
`integration_mdm_dep_test.go`, `integration_vpp_install_test.go`) whose
activity-detail and host-feed assertions changed now that `mdm_enrolled`
carries `host_id` and appears on the host timeline (feed assertions now
filter by activity type).
- **Pending on-device QA (next week):** DEP/ADE macOS and account-driven
user enrollment (iOS/iPadOS) on real hardware, per the issue's test
plan.
- Regression: Windows `mdm_enrolled` payload is unchanged (`host_id` is
omitted when zero); both platforms' `mdm_unenrolled` are unaffected.

# Screenshot for the frontend change

<img width="706" height="382" alt="Screenshot 2026-07-28 at 11 16 57 AM"
src="https://github.com/user-attachments/assets/8f57d129-f819-4399-8754-18b397a49db8"
/>

# Checklist for submitter

- [x] Changes file added for user-visible changes in `changes/`.
See [Changes
files](https://github.com/fleetdm/fleet/blob/main/docs/Contributing/guides/committing-changes.md#changes-files)
for more information.

## Testing

- [x] Added/updated automated tests
- [ ] QA'd all new/changed functionality manually <!-- manual macOS
verified via simulator; DEP + real-device ADUE pending next week -->


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

## Summary by CodeRabbit

* **New Features**
* Added support for rendering “MDM enrolled” in the host activity feed
with platform- and actor-aware messaging.

* **Bug Fixes**
* Updated Apple “MDM enrolled” activity details to include the correct
host identifier and serial/enrollment identifiers.
* Ensured host-scoped activity behavior applies only when the host is
known (host id present).

* **Tests**
* Expanded regression and integration coverage for “MDM enrolled”
activity details and feed contents, including VPP-related assertion
stability.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

---------

Co-authored-by: Magnus Jensen <magnus@fleetdm.com>

changes/49777-mdm-enrolled-host-id-apple.md

@@ -0,0 +1 @@
+- Added `host_id` and `host_serial` to the `mdm_enrolled` activity for Apple (macOS, iOS, iPadOS) enrollments, and the activity now appears on the host's activity timeline.