android: version tracks GOBLIN_BUILD, not GRIM's frozen 0.3.6

versionCode/versionName were inherited from GRIM (5 / "0.3.6") at the fork and
never rewired to Goblin's build number, so every build shipped as versionCode 5
- Android could not tell builds apart and Settings showed 0.3.6 for build 130.
Gradle now derives both from the GOBLIN_BUILD env (the same number the Rust side
stamps into crate::BUILD), with a fallback to the old values for a keyless local
gradle build.

android/app/build.gradle

@@ -11,8 +11,15 @@ android {
         applicationId "st.goblin.wallet"
         minSdk 24
         targetSdk 36
-        versionCode 5
+        // Version tracks Goblin's build number (GOBLIN_BUILD) so the Android
-        versionName "0.3.6"
+        // package identity moves forward with every release instead of freezing.
+        // Same env the Rust side stamps into crate::BUILD; the in-app updater
+        // compares build numbers, and this keeps versionCode (Android's
+        // upgrade/downgrade integer) in lockstep. Bare local gradle → fallback.
+        // ponytail: fallback keeps a keyless ./gradlew working; CI/release sets the env
+        def goblinBuild = (System.getenv("GOBLIN_BUILD") ?: "").trim()
+        versionCode goblinBuild.isEmpty() ? 5 : goblinBuild.toInteger()
+        versionName goblinBuild.isEmpty() ? "0.3.6" : goblinBuild
     }
 
     lint {