feat(android): :app module skeleton — Compose Activity + manifest

M8 phase 1.2. AndroidManifest declares FGS mediaPlayback +
POST_NOTIFICATIONS permissions ahead of the player phase. Activity
hosts a single Compose Scaffold for now; nav graph lands in phase 5.

Launcher icons reused from flutter_client/ (same applicationId means
same brand at cutover). MinstrelApplication referenced in manifest
but the class itself lands in Task 1.3 — manifest class names are
resolved at install time, not build time, so the intermediate commit
still builds.

@AndroidEntryPoint deferred to Task 1.3 alongside @HiltAndroidApp on
MinstrelApplication (Hilt KSP errors without an annotated Application).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

android/app/proguard-rules.pro

@@ -0,0 +1,19 @@
+# Keep the entry classes
+-keep class com.fabledsword.minstrel.MainActivity { *; }
+-keep class com.fabledsword.minstrel.MinstrelApplication { *; }
+
+# kotlinx.serialization (from the kotlinx.serialization README)
+-keepattributes *Annotation*, InnerClasses
+-dontnote kotlinx.serialization.AnnotationsKt
+-keepclassmembers class kotlinx.serialization.json.** {
+    *** Companion;
+}
+-keepclasseswithmembers class kotlinx.serialization.json.** {
+    kotlinx.serialization.KSerializer serializer(...);
+}
+
+# Hilt
+-keep class * extends androidx.lifecycle.ViewModel { *; }
+
+# Media3 — keep player/exo classes
+-keep class androidx.media3.** { *; }