Require passphrase confirmation for autobackup setting and encrypted export

A typo in a write-only passphrase field encrypts every backup with a
phrase the user cannot reproduce — unrecoverable by design. Both the
settings field and the manual-export dialog now demand a matching
repeat before accepting. Import is unchanged (wrong passphrase there
just fails loudly).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

app/src/main/java/no/naiv/meddetsamme/ui/SettingsScreen.kt

@@ -62,6 +62,7 @@ fun SettingsScreen(nav: Nav) {
     var accessKey by remember { mutableStateOf(settings.s3AccessKey ?: "") }
     var secretKey by remember { mutableStateOf(settings.s3SecretKey ?: "") }
     var autoPassphrase by remember { mutableStateOf(settings.autoBackupPassphrase ?: "") }
+    var autoPassphraseConfirm by remember { mutableStateOf(settings.autoBackupPassphrase ?: "") }
     var festUrl by remember { mutableStateOf(settings.festUrl ?: "") }
 
     // Export/import passphrase dialogs hold the pending document URI.
@@ -134,8 +135,24 @@ fun SettingsScreen(nav: Nav) {
                 },
                 modifier = Modifier.fillMaxWidth(),
             )
+            // Confirmation field: a typo here would encrypt every backup with a
+            // passphrase the user can't reproduce — unrecoverable by design.
+            val passphraseMismatch = autoPassphrase != autoPassphraseConfirm
+            OutlinedTextField(
+                value = autoPassphraseConfirm, onValueChange = { autoPassphraseConfirm = it },
+                label = { Text("Gjenta passordfrase") }, singleLine = true,
+                visualTransformation = PasswordVisualTransformation(),
+                keyboardOptions = KeyboardOptions(keyboardType = KeyboardType.Password),
+                isError = passphraseMismatch,
+                supportingText = { if (passphraseMismatch) Text("Passordfrasene er ikke like") },
+                modifier = Modifier.fillMaxWidth(),
+            )
             Button(
                 onClick = {
+                    if (passphraseMismatch) {
+                        toast("Passordfrasene er ikke like")
+                        return@Button
+                    }
                     settings.s3Endpoint = endpoint.trim().ifBlank { null }
                     settings.s3Region = region.trim().ifBlank { null }
                     settings.s3Bucket = bucket.trim().ifBlank { null }
@@ -144,6 +161,7 @@ fun SettingsScreen(nav: Nav) {
                     settings.autoBackupPassphrase = autoPassphrase.ifBlank { null }
                     toast("Lagret")
                 },
+                enabled = !passphraseMismatch,
                 modifier = Modifier.fillMaxWidth(),
             ) { Text("Lagre backupinnstillinger") }
 
@@ -214,6 +232,7 @@ fun SettingsScreen(nav: Nav) {
             title = "Krypter eksport",
             text = "Skriv en passordfrase (lagres ikke). La stå tom for ukryptert JSON.",
             allowEmpty = true,
+            requireConfirmation = true, // a typo here = an unrecoverable export
             onDismiss = { exportUri = null },
         ) { passphrase ->
             exportUri = null
@@ -306,10 +325,13 @@ private fun PassphraseDialog(
     title: String,
     text: String,
     allowEmpty: Boolean,
+    requireConfirmation: Boolean = false,
     onDismiss: () -> Unit,
     onConfirm: (CharArray) -> Unit,
 ) {
     var value by remember { mutableStateOf("") }
+    var repeated by remember { mutableStateOf("") }
+    val mismatch = requireConfirmation && value != repeated
     AlertDialog(
         onDismissRequest = onDismiss,
         title = { Text(title) },
@@ -324,12 +346,24 @@ private fun PassphraseDialog(
                     visualTransformation = PasswordVisualTransformation(),
                     keyboardOptions = KeyboardOptions(keyboardType = KeyboardType.Password),
                 )
+                if (requireConfirmation) {
+                    OutlinedTextField(
+                        value = repeated,
+                        onValueChange = { repeated = it },
+                        label = { Text("Gjenta passordfrase") },
+                        singleLine = true,
+                        isError = mismatch,
+                        supportingText = { if (mismatch) Text("Passordfrasene er ikke like") },
+                        visualTransformation = PasswordVisualTransformation(),
+                        keyboardOptions = KeyboardOptions(keyboardType = KeyboardType.Password),
+                    )
+                }
             }
         },
         confirmButton = {
             TextButton(
                 onClick = { onConfirm(value.toCharArray()) },
-                enabled = allowEmpty || value.isNotEmpty(),
+                enabled = (allowEmpty || value.isNotEmpty()) && !mismatch,
             ) { Text("OK") }
         },
         dismissButton = { TextButton(onClick = onDismiss) { Text("Avbryt") } },