dev-updater: build an app on the machine, install it on the phone

A Rust backend that discovers Android projects under configured roots,
builds one on request, and serves the APK over pinned TLS on a WireGuard
interface; an Android client that lists what is buildable, watches a build,
and installs the result. Enrolment carries the token and the CA, so the
phone trusts exactly the machine that issued it and nothing else.

`AGENTS.md` is the working guide and `README.md` the configuration
reference. The shared tunnel-and-TLS code lives in `vendor/wg-app-link`,
which ai-app uses too.

History before this point was squashed away, and a stale `config.json` went
with it: nothing had read that file since the config moved to RON outside
the checkout, and what it still held was one machine's absolute paths and
the names of projects on it.

test-projects/hello-app/.dev-updater.ron

@@ -0,0 +1,17 @@
+// A test project for Dev Updater, not a real app. See ../README.md.
+//
+// The plain case: one APK component, one variant, and nothing said about
+// resources -- which is itself the thing being tested here, since an
+// uninstall dialog for this project has to show its data and config toggles
+// disabled and say *why*, distinguishably from a project whose resources
+// could not be read.
+label: "Test: Hello",
+
+components: [
+    Apk(
+        name: "app",
+        // The list form rather than a line, because the label has a space
+        // in it and the line form splits on whitespace.
+        build: ["../lib/build-apk.sh", "--package", "com.example.dutest.hello", "--label", "Test Hello"],
+    ),
+],