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" />