Scan the enrollment QR in-app instead of relying on the camera app

Not every phone's camera app hands a scanned aiapp:// URI off to the app
reliably, which made enrollment an annoying multi-step process. The
Settings screen now scans the QR itself via zxing-android-embedded's
ScanContract (offline, no Play Services/ML Kit download) and feeds the
decoded URI through the existing parseEnrollmentUri. The aiapp://enroll
deep link stays as a fallback for cameras that do redirect.

Verified on the emulator: Scan QR code launches the scanner, prompts for
camera permission, shows a live preview, and backing out returns to
Settings cleanly.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017xn8nHw1tw1R6PtiY1eEtw

app/androidApp/src/main/AndroidManifest.xml

@@ -27,8 +27,12 @@
                 <category android:name="android.intent.category.LAUNCHER" />
             </intent-filter>
             <!-- Enrollment: the server prints its aiapp://enroll QR to the
-                 terminal; the phone's camera app opens the URI here, so no
-                 camera code or QR library is needed in this app. -->
+                 terminal. This intent filter is the fallback path for a
+                 camera app that redirects a scanned aiapp:// URI here
+                 directly; the Settings screen's own "Scan QR code" button
+                 (zxing-android-embedded) is the primary path and needs no
+                 filter, since it decodes the QR itself and hands the URI
+                 to parseEnrollmentUri in-process. -->
             <intent-filter>
                 <action android:name="android.intent.action.VIEW" />
                 <category android:name="android.intent.category.DEFAULT" />

app/androidApp/src/main/kotlin/com/example/aiapp/SettingsScreen.kt

@@ -1,5 +1,6 @@
 package com.example.aiapp
 
+import android.net.Uri
 import androidx.compose.foundation.layout.Column
 import androidx.compose.foundation.layout.Row
 import androidx.compose.foundation.layout.Spacer
@@ -9,6 +10,7 @@ import androidx.compose.foundation.layout.height
 import androidx.compose.foundation.layout.padding
 import androidx.compose.material3.Button
 import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.OutlinedButton
 import androidx.compose.material3.OutlinedTextField
 import androidx.compose.material3.Text
 import androidx.compose.material3.TextButton
@@ -21,12 +23,16 @@ import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.platform.LocalContext
 import androidx.compose.ui.unit.dp
+import androidx.activity.compose.rememberLauncherForActivityResult
+import com.journeyapps.barcodescanner.ScanContract
+import com.journeyapps.barcodescanner.ScanIntentResult
+import com.journeyapps.barcodescanner.ScanOptions
 
 /**
- * Server address and token. The normal path is scanning the server's
- * terminal QR (which lands in MainActivity and never shows this screen);
- * these fields are the fallback for typing the same three values by hand.
- * [onBack] is null on first run, when there is nothing to go back to.
+ * Server address and token. The normal path is the "Scan QR code" button
+ * below, which decodes the server's terminal QR itself; these fields are
+ * the fallback for typing the same three values by hand. [onBack] is null
+ * on first run, when there is nothing to go back to.
  */
 @Composable
 fun SettingsScreen(
@@ -42,6 +48,19 @@ fun SettingsScreen(
     var token by remember { mutableStateOf("") }
     var error by remember { mutableStateOf<String?>(null) }
 
+    val scanLauncher = rememberLauncherForActivityResult(ScanContract()) { result: ScanIntentResult ->
+        // Null contents means the user backed out of the scanner -- not an
+        // error, so nothing to report.
+        val contents = result.contents ?: return@rememberLauncherForActivityResult
+        val settings = parseEnrollmentUri(Uri.parse(contents))
+        if (settings == null) {
+            error = "Not a valid enrollment code"
+        } else {
+            saveServerSettings(context, settings)
+            onSaved(settings)
+        }
+    }
+
     Column(Modifier.fillMaxSize().padding(16.dp)) {
         Row(verticalAlignment = Alignment.CenterVertically, modifier = Modifier.fillMaxWidth()) {
             Text(
@@ -55,13 +74,19 @@ fun SettingsScreen(
         }
         Spacer(Modifier.height(8.dp))
         Text(
-            "The easy way: run ai-server on the backend and scan the QR it prints " +
-                "with the phone's camera. Or type the same values here.",
+            "The easy way: run ai-server on the backend and scan the QR it prints. " +
+                "Or type the same values here.",
             style = MaterialTheme.typography.bodyMedium,
             color = MaterialTheme.colorScheme.onSurfaceVariant,
         )
         Spacer(Modifier.height(16.dp))
 
+        OutlinedButton(
+            onClick = { scanLauncher.launch(ScanOptions().setDesiredBarcodeFormats(ScanOptions.QR_CODE)) },
+            modifier = Modifier.fillMaxWidth(),
+        ) { Text("Scan QR code") }
+        Spacer(Modifier.height(16.dp))
+
         OutlinedTextField(
             value = host,
             onValueChange = { host = it },