Refactor Android CI workflow to use Nix actions and improve translation file collection

android/app/build.gradle

@@ -23,11 +23,37 @@ if (flutterVersionName == null) {
 }
 
 def keystoreProperties = new Properties()
+// Prefer root key.properties, but fall back to android/key.properties if present (CI may place it there)
 def keystorePropertiesFile = rootProject.file('key.properties')
+if (!keystorePropertiesFile.exists()) {
+    def alt = rootProject.file('android/key.properties')
+    if (alt.exists()) {
+        keystorePropertiesFile = alt
+    }
+}
 if (keystorePropertiesFile.exists()) {
     keystoreProperties.load(new FileInputStream(keystorePropertiesFile))
+} 
+
+// Temporary debug task: prints which keystore file Gradle sees and whether the storeFile exists (does NOT print secrets)
+task printSigning {
+    doLast {
+        println "keystorePropertiesFile = ${keystorePropertiesFile}"
+        println "keystoreProperties keys = " + keystoreProperties.keySet().toString()
+        def store = keystoreProperties['storeFile']
+        println "storeFile = " + (store ?: 'null')
+        if (store) {
+            def f = new File(store)
+            println "storeFile absolute = " + f.absolutePath
+            println "storeFile exists = " + f.exists()
+            // Also show whether the file exists when interpreted relative to the Gradle rootProject
+            def f2 = new File(rootProject.projectDir, store)
+            println "storeFile relative to rootProject = " + f2.absolutePath + " exists = " + f2.exists()
+        }
+    }
 }
 
+
 android {
     namespace "inventree.inventree_app"
     compileSdkVersion 35