app: Scaffold Android TV PeerTube client (MVP)

Start the SmartTube-inspired PeerTube TV client as a Kotlin + Compose
for TV app. It targets any PeerTube instance (v1 API), with JTube as
the default, and covers login 0, local/own video listings 1-2, search
3, subscriptions 4, server-backed history 5 and HLS/progressive
playback with watching reports 6.

Password is only used for the OAuth password grant and never stored;
tokens are kept in EncryptedSharedPreferences. Building needs JDK 17+
(see README); the Gradle wrapper is checked in so no local Gradle is
required.

app/proguard-rules.pro

@@ -0,0 +1,17 @@
+# Keep kotlinx-serialization generated serializers
+-keepattributes *Annotation*, InnerClasses
+-dontnote kotlinx.serialization.AnnotationsKt
+
+-keepclassmembers class kotlinx.serialization.json.** {
+    *** Companion;
+}
+-keepclasseswithmembers class kotlinx.serialization.json.** {
+    kotlinx.serialization.KSerializer serializer(...);
+}
+-keep,includedescriptorclasses class net.jeena.jtubetv.**$$serializer { *; }
+-keepclassmembers class net.jeena.jtubetv.** {
+    *** Companion;
+}
+-keepclasseswithmembers class net.jeena.jtubetv.** {
+    kotlinx.serialization.KSerializer serializer(...);
+}