android: load release signing from keystore.properties

Read upload-keystore credentials from a gitignored keystore.properties
(falling back to unsigned release when absent), bundle full native debug
symbols for Play crash symbolication, and ignore keystore secrets.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

android/.gitignore

@@ -11,3 +11,8 @@
 
 # Local build artifacts
 *.apk
+
+# Signing — never commit the keystore or its passwords
+keystore.properties
+*.jks
+*.keystore

android/app/build.gradle.kts

@@ -1,3 +1,6 @@
+import java.io.FileInputStream
+import java.util.Properties
+
 plugins {
     alias(libs.plugins.android.application)
     alias(libs.plugins.kotlin.android)
@@ -6,6 +9,14 @@ plugins {
     alias(libs.plugins.ksp)
 }
 
+// Release signing credentials, loaded from android/keystore.properties (gitignored).
+// Falls back to no release signing when the file/keystore is absent (e.g. CI without secrets).
+val keystoreProps = Properties().apply {
+    val f = rootProject.file("keystore.properties")
+    if (f.exists()) load(FileInputStream(f))
+}
+val hasReleaseSigning = keystoreProps.getProperty("storeFile")?.let { file(it).exists() } == true
+
 android {
     namespace = "app.voltplan.cable"
     compileSdk = 35
@@ -25,17 +36,35 @@ android {
         resourceConfigurations += listOf("en", "de", "es", "fr", "nl")
     }
 
+    signingConfigs {
+        if (hasReleaseSigning) {
+            create("release") {
+                storeFile = file(keystoreProps.getProperty("storeFile"))
+                storePassword = keystoreProps.getProperty("storePassword")
+                keyAlias = keystoreProps.getProperty("keyAlias")
+                keyPassword = keystoreProps.getProperty("keyPassword")
+            }
+        }
+    }
+
     buildTypes {
         debug {
             isMinifyEnabled = false
         }
         release {
+            if (hasReleaseSigning) {
+                signingConfig = signingConfigs.getByName("release")
+            }
             isMinifyEnabled = true
             isShrinkResources = true
             proguardFiles(
                 getDefaultProguardFile("proguard-android-optimize.txt"),
                 "proguard-rules.pro",
             )
+            // Bundle native debug symbols so Play can symbolicate native crashes/ANRs.
+            ndk {
+                debugSymbolLevel = "FULL"
+            }
         }
     }