Sign release builds with a dedicated release key

- Add a release signing config that reads keystore.properties when present
- Keep debug builds working when the key file is absent
- Enable v2 and v3 signature schemes so the key can be rotated later
- Ignore keystores and keystore.properties so secrets stay out of the repo

.gitignore

@@ -33,3 +33,9 @@ release/FlexCam-Windows.zip
 
 # Personal handoff/backup note (not for the repo)
 FLEXCAM-HANDOFF.md
+
+# Signing keys and secrets (never commit)
+*.jks
+*.keystore
+keystore.properties
+android/keystore.properties

android/app/build.gradle.kts

@@ -1,9 +1,18 @@
+import java.io.FileInputStream
+import java.util.Properties
+
 plugins {
     id("com.android.application")
     id("org.jetbrains.kotlin.android")
 }
 
 android {
+    val keystorePropertiesFile = rootProject.file("keystore.properties")
+    val keystoreProperties = Properties()
+    if (keystorePropertiesFile.exists()) {
+        keystoreProperties.load(FileInputStream(keystorePropertiesFile))
+    }
+
     namespace = "com.flexcam"
     compileSdk = 36
 
@@ -15,9 +24,25 @@ android {
         versionName = "1.3"
     }
 
+    signingConfigs {
+        if (keystorePropertiesFile.exists()) {
+            create("release") {
+                storeFile = file(keystoreProperties["storeFile"] as String)
+                storePassword = keystoreProperties["storePassword"] as String
+                keyAlias = keystoreProperties["keyAlias"] as String
+                keyPassword = keystoreProperties["keyPassword"] as String
+                enableV2Signing = true
+                enableV3Signing = true
+            }
+        }
+    }
+
     buildTypes {
         release {
             isMinifyEnabled = false
+            if (keystorePropertiesFile.exists()) {
+                signingConfig = signingConfigs.getByName("release")
+            }
         }
     }