Set up project skeleton (milestone 1)

- Architecture and feature overview in docs/ARCHITECTURE.md
- Gradle 9.8 / AGP 9.4 / Kotlin 2.4 with version catalog and convention plugins
- Modules :app, :core:*, :device-profiles, :feature:* (placeholder screens)
- Flavors core (no INTERNET, enforced by a build check) and full
- Material You theme, navigation, expert mode and dry-run settings (DataStore)
- Pixel 8-10 device detection, unit tests, GPLv3 license, English README with Obtainium badge

Co-Authored-By: Claude Opus 5.5 <[email protected]>

build-logic/convention/src/main/kotlin/JvmLibraryConventionPlugin.kt

@@ -0,0 +1,23 @@
+import org.gradle.api.Plugin
+import org.gradle.api.Project
+import org.gradle.api.plugins.JavaPluginExtension
+import org.gradle.kotlin.dsl.configure
+import org.gradle.kotlin.dsl.dependencies
+
+class JvmLibraryConventionPlugin : Plugin<Project> {
+    override fun apply(target: Project) = with(target) {
+        pluginManager.apply("org.jetbrains.kotlin.jvm")
+        pluginManager.apply("com.android.lint")
+        extensions.configure<JavaPluginExtension> {
+            sourceCompatibility = JAVA_VERSION
+            targetCompatibility = JAVA_VERSION
+        }
+        configureKotlin()
+        dependencies {
+            add("testImplementation", libs.lib("junit"))
+            add("testImplementation", libs.lib("truth"))
+            add("testImplementation", libs.lib("kotlinx-coroutines-test"))
+            add("testImplementation", libs.lib("turbine"))
+        }
+    }
+}