Add release signing config

Reads keystore credentials from a gitignored key.properties so
release builds are signed consistently instead of debug-signed,
which lets future releases install as updates over old ones.

Author: roman-gmk

app/build.gradle

@@ -3,6 +3,12 @@ plugins {
     id 'kotlin-android'
 }
 
+def keystoreProperties = new Properties()
+def keystorePropertiesFile = rootProject.file('key.properties')
+if (keystorePropertiesFile.exists()) {
+    keystoreProperties.load(new FileInputStream(keystorePropertiesFile))
+}
+
 android {
     namespace 'com.sleepbutton.app'
     compileSdk 34
@@ -15,11 +21,23 @@ android {
         versionName "1.0"
     }
 
+    signingConfigs {
+        release {
+            if (keystorePropertiesFile.exists()) {
+                storeFile file(keystoreProperties['storeFile'])
+                storePassword keystoreProperties['storePassword']
+                keyAlias keystoreProperties['keyAlias']
+                keyPassword keystoreProperties['keyPassword']
+            }
+        }
+    }
+
     buildTypes {
         release {
             minifyEnabled true
             shrinkResources true
             proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
+            signingConfig signingConfigs.release
         }
     }