Clarify Add hosts modal: fleetctl generates installer, not run on hosts (#41055)

## Summary

- Changes label text from "Run this command with the Fleet command-line
tool" to "Generate your installer with the Fleet command-line tool" —
making clear the command produces an installer package, not something
run on each host
- Adds help text to Windows (MSI), Linux (deb), and macOS (pkg) tabs:
"Run this on your admin computer, then deploy the generated package to
your hosts"

## Problem

Customer feedback: users believe they need to install both `fleetctl`
and the enrollment package on each host they're enrolling. The old copy
didn't convey that:
1. `fleetctl package` is run once on an admin machine (not on hosts)
2. The output is a deployable installer package that goes to the hosts

## Test plan

- [ ] Open the Add hosts modal on macOS, Windows, and Linux tabs
- [ ] Confirm label reads "Generate your installer with the Fleet
command-line tool"
- [ ] Confirm help text below the command reads "Run this on your admin
computer, then deploy the generated package to your hosts"
- [ ] Confirm the Advanced tab label is also updated
- [ ] Confirm plain-osquery path is unaffected (no label shown)
- [ ] Confirm ChromeOS, iOS & iPadOS, Android tabs are unaffected

frontend/components/AddHostsModal/PlatformWrapper/PlatformWrapper.tsx

@@ -240,7 +240,7 @@ const PlatformWrapper = ({
       <>
         {packageType !== "plain-osquery" && (
           <span className={`${baseClass}__cta`}>
-            Run this command with the{" "}
+            Generate your installer with the{" "}
             <CustomLink
               className={`${baseClass}__command-line-tool`}
               url={`${LEARN_MORE_ABOUT_BASE_LINK}/installing-fleetctl`}
@@ -271,19 +271,23 @@ const PlatformWrapper = ({
     if (packageType === "deb") {
       packageTypeHelpText = (
         <>
-          For CentOS, Red Hat, and Fedora Linux, use <code>--type=rpm</code>.
-          For Arch Linux, use <code>--type=pkg.tar.zst</code>.<br />
+          Run this on your admin computer, then deploy the generated package to
+          your hosts. For CentOS, Red Hat, and Fedora Linux, use{" "}
+          <code>--type=rpm</code>. For Arch Linux, use{" "}
+          <code>--type=pkg.tar.zst</code>.<br />
           For ARM, use <code>--arch=arm64</code>
         </>
       );
     } else if (packageType === "msi") {
       packageTypeHelpText = (
         <>
-          For ARM, use <code>--arch=arm64</code>
+          Run this on your admin computer, then deploy the generated package to
+          your hosts. For ARM, use <code>--arch=arm64</code>
         </>
       );
     } else if (packageType === "pkg") {
-      packageTypeHelpText = "Install this package to add hosts to Fleet.";
+      packageTypeHelpText =
+        "Run this on your admin computer, then install the generated package on your hosts.";
     } else {
       packageTypeHelpText = "";
     }