feat(android): add native Android client

Kotlin + Jetpack Compose client for a self-hosted instance: manual
server setup and health check, auth with Keystore-backed tokens, album
and photo browsing with SSE live updates, upload queue in WorkManager
with HEIC-to-JPEG conversion, and Room/Coil offline cache. Add an
android Makefile target and revise project.md §17.

android/gradle/wrapper/gradle-wrapper.properties

@@ -0,0 +1,7 @@
+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-8.9-bin.zip
+networkTimeout=10000
+validateDistributionUrl=true
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists