Ask Dev Updater for the checkout, not for the app inside it

Dev Updater's unit is a project -- a directory in a checkout -- that
produces components, so this declaration belongs at the repository root
where it can say where each half lives. `cwd` is how a component says
that, and it is what the old file was working around: sitting in `app/`,
it reached the backend with `../server/Cargo.toml` and `../server/service`,
which described the layout backwards.

So the file says what this repository produces: the backend, built and
serviced in `server/`, and then the APK, built in `app/`. The order is
unchanged and still the point -- a failing APK build leaves the phone the
APK it already had rather than half of a matched pair.

The service script gains dev-updater's note about lingering. A user
service stops at logout unless `loginctl enable-linger` is set, which for
this one matters more than for a build server: the phone reaches ai-server
whether or not anyone is logged in at the desk.

**This changes the project path, so the phone's existing entry (at
~/repos/ai-app/app) has to be removed and the checkout root added
instead**, and its components accepted once.

Verified against dev-updater's current parser rather than by reading its
schema: the declaration loads, `cargo build --release` resolves into
server/, app/build-apk.sh into app/, the service script to an absolute
path, and APK discovery from the root still finds the built APK.
`./server/service status` prints not-installed and exits 0.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017xn8nHw1tw1R6PtiY1eEtw

app/.dev-updater.ron

@@ -1,21 +0,0 @@
-// Read by Dev Updater. Structured as the body of the config: no outer
-// parentheses, so nothing here is indented for the sake of a wrapper.
-
-label: "AI Sessions",
-
-// The server is built and delivered before the APK: if the APK build then
-// fails, the phone keeps being offered the one it already had rather than
-// half of a matched pair.
-components: [
-    Server(
-        name: "backend",
-        build: "cargo build --release --manifest-path ../server/Cargo.toml",
-        // Installs into whichever user-service manager is here, and is how
-        // this server is started, stopped and asked about. See the script.
-        service: "../server/service",
-    ),
-    Apk(
-        name: "app",
-        build: "./build-apk.sh",
-    ),
-]