- Migrate build system to Kotlin DSL (build.gradle.kts, settings.gradle.kts)

- Upgrade `compileSdk` and `targetSdk` to 36
- Add German (`de`) localization and string resources
- Add Michachatz F-Droid repository to default list
- Update dependencies and plugins in `libs.versions.toml`
- Remove manual signing configuration from README.md
- Refactor code to use non-deprecated `alpha` property and context-based string retrieval
- Clean up `buildConfig` and locale filtering logic

build.gradle.kts

@@ -0,0 +1,80 @@
+plugins {
+    alias(libs.plugins.android.application)
+}
+
+android {
+    namespace = "com.michatec.store"
+    compileSdk = 36
+
+    defaultConfig {
+        applicationId = "com.michatec.store"
+        minSdk = 30
+        targetSdk = 36
+        versionCode = 18
+        versionName = "1.8"
+
+        val languages = listOf("en", "de")
+        buildConfigField("String[]", "LANGUAGES", "{ \"${languages.joinToString("\", \"")}\" }")
+
+        @Suppress("UnstableApiUsage")
+        androidResources {
+            localeFilters += languages
+        }
+    }
+
+    buildFeatures {
+        buildConfig = true
+    }
+
+    sourceSets {
+        getByName("main") {
+            kotlin.directories += "src/main/kotlin"
+        }
+    }
+
+    compileOptions {
+        sourceCompatibility = JavaVersion.VERSION_17
+        targetCompatibility = JavaVersion.VERSION_17
+    }
+
+    flavorDimensions += "distributor"
+    productFlavors {
+        create("michas") {
+            dimension = "distributor"
+            buildConfigField("boolean", "FLAVOR_FDROID", "false")
+        }
+        create("fdroid") {
+            dimension = "distributor"
+            buildConfigField("boolean", "FLAVOR_FDROID", "true")
+        }
+    }
+
+    buildTypes {
+        getByName("debug") {
+            isMinifyEnabled = false
+            isShrinkResources = false
+        }
+        getByName("release") {
+            isMinifyEnabled = true
+            isShrinkResources = false
+            proguardFiles(
+                getDefaultProguardFile("proguard-android-optimize.txt"),
+                "proguard.pro"
+            )
+        }
+    }
+}
+
+dependencies {
+    implementation(libs.kotlin.stdlib)
+    implementation(libs.core.ktx)
+    implementation(libs.fragment.ktx)
+    implementation(libs.viewpager2)
+    implementation(libs.vectordrawable)
+    implementation(libs.okhttp)
+    implementation(libs.rxjava)
+    implementation(libs.rxandroid)
+    implementation(libs.jackson.core)
+    implementation(libs.picasso)
+    implementation(libs.freedroidwarn)
+}