Optimize IsHostConnectedToFleetMDM on the orbit check-in hot path (#44629) (#48375)

**Related issue:** Resolves #44629

This folds the connected-to-Fleet check into `GetHostMDM` via a
`connected_to_fleet` column that mirrors the existing
`IsHostConnectedToFleetMDM` and `hostMDMSelect` conditions, and derives
the value in `GetOrbitConfig` from the `host_mdm` data it already
fetches. Result: **2 queries → 1** on the orbit check-in hot path, with
no semantic change.

# Checklist for submitter

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

- [x] Input data is properly validated, `SELECT *` is avoided, SQL
injection is prevented (using placeholders for values in statements), JS
inline code is prevented especially for url redirects, and untrusted
data interpolated into shell scripts/commands is validated against shell
metacharacters.

## 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)
- [x] QA'd all new/changed functionality manually


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

## Summary by CodeRabbit

* **Performance Improvements**
* Orbit check-ins now determine MDM connection status from existing host
MDM data, reducing database work and improving response time.
* **Bug Fixes**
* Added platform-aware connection detection so Windows, Apple, and
Android devices report MDM connectivity more accurately.
* Updated related checks and tests to keep connection status consistent
across enrollment and unenrollment changes.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

changes/44629-optimize-orbit-mdm-connection-check

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+* Improved orbit check-in performance by deriving the Fleet MDM connection state from existing host MDM data instead of running a separate 3-table JOIN query on every check-in for every host.