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.

.gitignore

@@ -16,3 +16,14 @@ __pycache__/
 galo.db
 galo.db-*
 data/
+
+# Android build output and local toolchain config
+android/.gradle/
+android/build/
+android/app/build/
+android/local.properties
+android/keystore.properties
+android/*.jks
+android/*.keystore
+android/.idea/
+android/captures/