Add native Kotlin/Compose Android port

Full feature-parity port of the iOS app under ./android (package
app.voltplan.cable): Systems, bottom-nav system detail (Overview,
Components, Batteries, Chargers), calculator/loads, battery & charger
editors, overview with runtime/charge goals, Bill of Materials with PDF
export, VoltPlan PocketBase component library, and Aptabase analytics.
Room persistence, 5-language localization. Verified to build (assembleDebug).

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

android/gradle.properties

@@ -0,0 +1,6 @@
+org.gradle.jvmargs=-Xmx2048m -Dfile.encoding=UTF-8
+org.gradle.caching=true
+org.gradle.configuration-cache=true
+android.useAndroidX=true
+kotlin.code.style=official
+android.nonTransitiveRClass=true