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>

xtask/Cargo.lock

@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 4
+
+[[package]]
+name = "xtask"
+version = "0.1.0"