feat: scaffold Android terminal POS app (RewardFlow Terminal)

Native Android tablet app for loyalty POS terminal. Replaces web
terminal for merchants who need device lockdown, camera QR scanning,
and offline operation.

Project at apps/terminal-android/ — Kotlin, Jetpack Compose, calls
the same /api/v1/store/loyalty/* API (no backend changes).

Scaffold includes:
- Gradle build (Kotlin DSL) with version catalog (libs.versions.toml)
- Hilt DI, Retrofit + Moshi networking, Room offline DB
- CameraX + ML Kit barcode scanning dependencies
- DataStore for device config persistence
- WorkManager for background sync
- Three-screen navigation: Setup → PIN → Terminal
- Stub screens with layout structure (ready to implement)
- API models matching all loyalty store endpoints
- PendingTransaction entity + DAO for offline queue
- RewardFlow brand theme (purple, light/dark)
- Landscape-only, fullscreen, Lock Task Mode ready
- SETUP.md with Android Studio installation guide
- .gitignore for Android build artifacts

Tech decisions:
- Min SDK 26 (Android 8.0, 95%+ tablet coverage)
- Firebase App Distribution for v1, Play Store later
- Staff PIN auth (no username/password on POS)
- One-time device setup via QR code from web settings

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/terminal-android/app/proguard-rules.pro

@@ -0,0 +1,7 @@
+# Moshi
+-keep class lu.rewardflow.terminal.data.model.** { *; }
+-keepclassmembers class lu.rewardflow.terminal.data.model.** { *; }
+
+# Retrofit
+-keepattributes Signature
+-keepattributes *Annotation*