Android: replace language free-text with a dropdown (auto/en/de)

Fixed list per current needs; "auto" passes null to the engine like
the desktop app. Live-mode model defaults (tiny/base live, small for
final) will follow with M2.

android/app/src/main/java/com/meetrec/android/MainActivity.kt

@@ -67,7 +67,8 @@ fun MeetRecScreen() {
 
     var model by remember { mutableStateOf("tiny") }
     var modelMenu by remember { mutableStateOf(false) }
-    var language by remember { mutableStateOf("") }
+    var language by remember { mutableStateOf("auto") }
+    var langMenu by remember { mutableStateOf(false) }
     var status by remember { mutableStateOf("Select a model, download and load it.") }
     var busy by remember { mutableStateOf(false) }
     var engine by remember { mutableStateOf<WhisperEngine?>(null) }
@@ -196,13 +197,28 @@ fun MeetRecScreen() {
                     }
                 }
             }
-            OutlinedTextField(
-                value = language,
-                onValueChange = { language = it.trim() },
-                label = { Text("Language") },
-                placeholder = { Text("auto") },
+            ExposedDropdownMenuBox(
+                expanded = langMenu,
+                onExpandedChange = { langMenu = it },
                 modifier = Modifier.weight(1f),
-            )
+            ) {
+                OutlinedTextField(
+                    value = language,
+                    onValueChange = {},
+                    readOnly = true,
+                    label = { Text("Language") },
+                    trailingIcon = { ExposedDropdownMenuDefaults.TrailingIcon(langMenu) },
+                    modifier = Modifier.menuAnchor().fillMaxWidth(),
+                )
+                ExposedDropdownMenu(expanded = langMenu, onDismissRequest = { langMenu = false }) {
+                    LANGUAGES.forEach { code ->
+                        DropdownMenuItem(
+                            text = { Text(code) },
+                            onClick = { language = code; langMenu = false },
+                        )
+                    }
+                }
+            }
         }
 
         // model actions
@@ -279,7 +295,7 @@ fun MeetRecScreen() {
                                 eng.transcribe(
                                     samples,
                                     beamSize = 5,
-                                    language = language.ifBlank { null },
+                                    language = language.takeIf { it != "auto" },
                                 )
                             }
                             segments = segs
@@ -326,6 +342,8 @@ fun MeetRecScreen() {
     }
 }
 
+private val LANGUAGES = listOf("auto", "en", "de")
+
 private fun fmtMs(ms: Long): String {
     val total = ms / 1000
     val h = total / 3600