fix(build): add explicit Kotlin imports for Properties/FileInputStream and fix signing config casts

- Add import statements for java.util.Properties and java.io.FileInputStream
  (newer Kotlin DSL requires explicit imports)
- Replace deprecated jvmTarget = JavaVersion.VERSION_17.toString() with "17"
- Replace unsafe 'as String' casts with Properties.getProperty() in signing config
- Fix same import issue in settings.gradle.kts

android/app/build.gradle.kts

@@ -1,3 +1,6 @@
+import java.util.Properties
+import java.io.FileInputStream
+
 plugins {
     id("com.android.application")
     id("kotlin-android")
@@ -14,9 +17,9 @@ dependencies {
 
 // Load release signing properties if key.properties exists (set by CI pipeline)
 val keystorePropertiesFile = rootProject.file("key.properties")
-val keystoreProperties = java.util.Properties()
+val keystoreProperties = Properties()
 if (keystorePropertiesFile.exists()) {
-    keystoreProperties.load(java.io.FileInputStream(keystorePropertiesFile))
+    keystoreProperties.load(FileInputStream(keystorePropertiesFile))
 }
 
 android {
@@ -30,7 +33,7 @@ android {
     }
 
     kotlinOptions {
-        jvmTarget = JavaVersion.VERSION_17.toString()
+        jvmTarget = "17"
     }
 
     defaultConfig {
@@ -47,10 +50,10 @@ android {
     signingConfigs {
         create("release") {
             if (keystorePropertiesFile.exists()) {
-                keyAlias = keystoreProperties["keyAlias"] as String
-                keyPassword = keystoreProperties["keyPassword"] as String
-                storeFile = file(keystoreProperties["storeFile"] as String)
-                storePassword = keystoreProperties["storePassword"] as String
+                keyAlias = keystoreProperties.getProperty("keyAlias")
+                keyPassword = keystoreProperties.getProperty("keyPassword")
+                storeFile = file(keystoreProperties.getProperty("storeFile"))
+                storePassword = keystoreProperties.getProperty("storePassword")
             }
         }
     }