Put the service script back until the switch can be sequenced

Reverts the switch to `service: Managed(...)`. The switch is still right
and the reasoning in that commit still holds; what was wrong was doing it
now, unilaterally, to a checkout something is reading live.

A dev-updater is running against this working tree, so deleting
`server/service` did not wait for a pull to take effect -- the backend
card went to "couldn't check -- failed to run the service script: No such
file or directory" immediately, and the pushed declaration still names the
script, so the tree and the declaration disagreed in the one direction
that breaks things. My own commit message had said this change was not
safe to pull blind; it turned out not to need a pull at all.

The switch needs three steps in order, and only the middle one is mine:
Uninstall from the backend card while the script is still declared, then
take the change, then Install. Re-apply when Iris is ready to do that,
which is also when dev-updater's conversion path can be deleted.

.dev-updater.ron

@@ -18,17 +18,9 @@ components: [
         name: "backend",
         build: "cargo build --release",
         cwd: "server",
-        // Dev Updater's own built-in service implementation, generated
-        // into its data directory and driven through the same interface a
-        // project-supplied script would be. ai-app carried a script of its
-        // own until 2026-08-28; it ran `target/release/ai-server` with no
-        // arguments and no environment, which is the generic case exactly,
-        // so it was two copies of one thing and the copy that could not be
-        // tested from here -- the OpenRC branch -- was duplicated with it.
-        //
-        // Resolved against this component's `cwd`, so this is
-        // `server/target/release/ai-server`.
-        service: Managed("target/release/ai-server"),
+        // Installs into whichever user-service manager is here, and is how
+        // ai-server is started, stopped and asked about. See the script.
+        service: "server/service",
     ),
     Apk(
         name: "app",