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/gradle/libs.versions.toml

@@ -1,5 +1,6 @@
 # Latest stable versions as of 2026-08-24 (checked against Google Maven /
-# Maven Central; prereleases deliberately skipped).
+# Maven Central; prereleases deliberately skipped). zxing-embedded checked
+# 2026-08-25.
 [versions]
 agp = "9.3.2"
 kotlin = "2.4.10"
@@ -7,9 +8,15 @@ compose-multiplatform = "1.11.1"
 # material3 ships on its own release train, separate from the CMP version.
 compose-material3 = "1.9.0"
 androidx-activityCompose = "1.13.0"
+zxing-embedded = "4.3.0"
 
 [libraries]
 androidx-activity-compose = { module = "androidx.activity:activity-compose", version.ref = "androidx-activityCompose" }
+# In-app QR scanner: a ready-made scanning Activity (camera preview, runtime
+# permission prompt, flashlight toggle) reached through the AndroidX Activity
+# Result API (ScanContract, added in 4.3.0). Fully offline -- no Play
+# Services / ML Kit model download involved.
+zxing-embedded = { module = "com.journeyapps:zxing-android-embedded", version.ref = "zxing-embedded" }
 # Declared directly rather than through the plugin's `compose.*` accessors,
 # which are deprecated as of CMP 1.11.
 compose-runtime = { module = "org.jetbrains.compose.runtime:runtime", version.ref = "compose-multiplatform" }