Ship a signed release APK

The release build type reuses the debug signing config, so a downloaded APK
installs over an existing one instead of demanding an uninstall. This never
goes to Play, which rejects debug keys anyway, so there is no private key
worth safeguarding for years and no way to strand anyone on a version that
can no longer be updated.

That choice is load-bearing in one direction: a release build is not
DEBUGGABLE, so adb shell run-as stops reading app data back out, and there is
no in-app restore. A signature change would have cost the drill progress.

npm run release stages release/404-Layers-<version>.apk with a checksum and
verifies the signature, since an unsigned APK builds fine and only fails at
install time, on someone else's phone.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

android/app/build.gradle

@@ -8,7 +8,7 @@ android {
         minSdkVersion rootProject.ext.minSdkVersion
         targetSdkVersion rootProject.ext.targetSdkVersion
         versionCode 1
-        versionName "1.0"
+        versionName "1.0.0"
         testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
         aaptOptions {
              // Files and dirs to omit from the packaged assets dir, modified to accommodate modern web apps.
@@ -20,6 +20,11 @@ android {
         release {
             minifyEnabled false
             proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
+            // Debug key on purpose: this only ever ships as a sideloaded APK, never
+            // to Play. Same signature as every build so far, so a release installs
+            // over an existing one instead of demanding an uninstall. Using the
+            // built-in config keeps the path and password out of this file.
+            signingConfig signingConfigs.debug
         }
     }
 }