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/app/build.gradle.kts

@@ -0,0 +1,89 @@
+plugins {
+    alias(libs.plugins.android.application)
+    alias(libs.plugins.kotlin.android)
+    alias(libs.plugins.kotlin.compose)
+    alias(libs.plugins.kotlin.serialization)
+    alias(libs.plugins.ksp)
+}
+
+android {
+    namespace = "app.voltplan.cable"
+    compileSdk = 35
+
+    defaultConfig {
+        applicationId = "app.voltplan.cable"
+        minSdk = 26
+        targetSdk = 35
+        versionCode = 1
+        versionName = "1.0"
+
+        // Aptabase analytics — mirrors the iOS configuration (the iPhone app's tracker).
+        buildConfigField("String", "APTABASE_APP_KEY", "\"A-SH-4260269603\"")
+        buildConfigField("String", "APTABASE_HOST", "\"https://apta.yuzuhub.com\"")
+
+        vectorDrawables { useSupportLibrary = true }
+        resourceConfigurations += listOf("en", "de", "es", "fr", "nl")
+    }
+
+    buildTypes {
+        debug {
+            isMinifyEnabled = false
+        }
+        release {
+            isMinifyEnabled = true
+            isShrinkResources = true
+            proguardFiles(
+                getDefaultProguardFile("proguard-android-optimize.txt"),
+                "proguard-rules.pro",
+            )
+        }
+    }
+
+    compileOptions {
+        sourceCompatibility = JavaVersion.VERSION_17
+        targetCompatibility = JavaVersion.VERSION_17
+    }
+    kotlinOptions {
+        jvmTarget = "17"
+    }
+    buildFeatures {
+        compose = true
+        buildConfig = true
+    }
+    packaging {
+        resources {
+            excludes += "/META-INF/{AL2.0,LGPL2.1}"
+        }
+    }
+}
+
+dependencies {
+    implementation(libs.androidx.core.ktx)
+    implementation(libs.androidx.lifecycle.runtime.ktx)
+    implementation(libs.androidx.lifecycle.runtime.compose)
+    implementation(libs.androidx.lifecycle.viewmodel.compose)
+    implementation(libs.androidx.activity.compose)
+
+    implementation(platform(libs.androidx.compose.bom))
+    implementation(libs.androidx.ui)
+    implementation(libs.androidx.ui.graphics)
+    implementation(libs.androidx.ui.tooling.preview)
+    implementation(libs.androidx.material3)
+    implementation(libs.androidx.material.icons.extended)
+    implementation(libs.androidx.navigation.compose)
+    debugImplementation(libs.androidx.ui.tooling)
+
+    implementation(libs.androidx.room.runtime)
+    implementation(libs.androidx.room.ktx)
+    ksp(libs.androidx.room.compiler)
+
+    implementation(libs.androidx.datastore.preferences)
+
+    implementation(libs.retrofit)
+    implementation(libs.retrofit.serialization)
+    implementation(libs.okhttp)
+    implementation(libs.okhttp.logging)
+    implementation(libs.kotlinx.serialization.json)
+
+    implementation(libs.coil.compose)
+}