Fix: Label shows outdated manually selected host after navigating back to the Edit page (#44216)

<!-- Add the related story/sub-task/bug number, like Resolves #123, or
remove if NA -->
**Related issue:** Resolves #43135

# 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.

## Testing

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


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

* **Bug Fixes**
* Fixed stale "Selected hosts" display on the edit label page by
ensuring host data refreshes after successful label edits, so the UI
reflects the updated host set immediately.
* Fixed stale host selections when navigating between manual labels by
scoping and resetting the form to the correct current host set,
preventing selections from carrying over between labels.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

changes/43135-fix-stale-label-hosts

@@ -0,0 +1,2 @@
+* Fixed stale "Selected hosts" on the edit label page after a previous edit by invalidating the related query caches on success.
+* Fixed stale "Selected hosts" on the edit label page when navigating between manual labels by scoping the hosts cache per label and keying the form on the actual host set.

frontend/pages/labels/EditLabelPage/EditLabelPage.tsx

@@ -79,7 +79,7 @@ const EditLabelPage = ({ routeParams, router }: IEditLabelPageProps) => {
     isLoading: isLoadingHosts,
     isError: isErrorHosts,
   } = useQuery<IGetHostsInLabelResponse, AxiosError, IHost[]>(
-    ["hosts"],
+    ["hosts", labelId],
     () => {
       return labelsAPI.getHostsInLabel(labelId);
     },
@@ -101,6 +101,8 @@ const EditLabelPage = ({ routeParams, router }: IEditLabelPageProps) => {
       await labelsAPI.update(labelId, formData);
       renderFlash("success", "Label updated successfully.");
       queryClient.invalidateQueries(["label", labelId, currentUser]);
+      queryClient.invalidateQueries(["hosts", labelId]);
+      queryClient.invalidateQueries(["labels"]);
     } catch (error) {
       const status = (error as { status: number }).status;
       let errorMessage = "Couldn't edit label. Please try again.";
@@ -150,7 +152,10 @@ const EditLabelPage = ({ routeParams, router }: IEditLabelPageProps) => {
       />
     ) : (
       <ManualLabelForm
-        key={targetedHosts?.toString()}
+        key={`${labelId}-${(targetedHosts || [])
+          .map((h) => h.id)
+          .sort((a, b) => a - b)
+          .join(",")}`}
         defaultName={label.name}
         defaultDescription={label.description}
         defaultTargetedHosts={targetedHosts}