E5: package app/shellApp without Gradle (cargo xtask apk)

New xtask/ crate (no deps) runs cargo ndk -> javac -> d8 -> aapt2 ->
zipalign -> apksigner directly, signed with the same key build-apk.sh
uses. Both pass conditions proved on the ai-app-2 emulator: the xtask
APK installs over the Gradle-built shellApp, and the notification
service starts and posts a real notification while backgrounded.

Adds one printRuntimeClasspathJars task to shellApp/build.gradle.kts
(and a matching signingConfig) -- the one disclosed Gradle call the
xtask still makes, to resolve the AndroidX/​:link dependency graph.
That call's Kotlin compilation of :link as a side effect also answers
E3's open kotlinc question, so no Java port of ServerStore was needed.
Wires a second Apk component into .dev-updater.ron beside the existing
one. Full writeup in RUST.md's E5 box.

Co-Authored-By: Claude Sonnet <noreply@anthropic.com>

.dev-updater.ron

@@ -55,4 +55,21 @@ components: [
         // the terminal the QR would be printed on.
         enroll: "server/enroll-link.sh",
     ),
+    // E5 (RUST.md): app/shellApp packaged by the xtask instead of Gradle
+    // (cargo ndk -> javac -> d8 -> aapt2 -> zipalign -> apksigner), signed
+    // with the same release key as "app" above so the two can install
+    // over each other -- a separate component, not a mode of "app" above,
+    // because it is a different applicationId (com.example.aiapp.shell)
+    // built by a different tool from different sources. No `cwd`: it
+    // defaults to this checkout's root, which both the `cargo xtask`
+    // alias (`.cargo/config.toml`, resolved relative to the working
+    // directory cargo is run from) and `cargo xtask apk`'s own publishing
+    // step (`xtask/build/outputs/apk/<mode>/*.apk`, matching discover.rs's
+    // `*/build/outputs/apk/*/*.apk` pattern -- see apk.rs's module doc)
+    // both need.
+    Apk(
+        name: "shell",
+        modes: ["release", "debug"],
+        build: "cargo xtask apk",
+    ),
 ],