Add signing configuration for APK installation

Added debug keystore signing for release builds to enable
installation on devices. Using Android debug keystore for now.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

app/build.gradle.kts

@@ -22,13 +22,27 @@ android {
         }
     }
 
+    signingConfigs {
+        create("release") {
+            // Using debug keystore for now - replace with your own keystore
+            storeFile = file("${System.getProperty("user.home")}/.android/debug.keystore")
+            storePassword = "android"
+            keyAlias = "androiddebugkey"
+            keyPassword = "android"
+        }
+    }
+
     buildTypes {
+        debug {
+            signingConfig = signingConfigs.getByName("debug")
+        }
         release {
             isMinifyEnabled = true
             proguardFiles(
                 getDefaultProguardFile("proguard-android-optimize.txt"),
                 "proguard-rules.pro"
             )
+            signingConfig = signingConfigs.getByName("release")
         }
     }