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/build.gradle.kts

@@ -0,0 +1,46 @@
+plugins {
+    `kotlin-dsl`
+}
+
+group = "org.pixelwall.buildlogic"
+
+java {
+    toolchain.languageVersion.set(JavaLanguageVersion.of(21))
+}
+
+dependencies {
+    compileOnly(libs.android.gradle.plugin)
+    compileOnly(libs.kotlin.gradle.plugin)
+    compileOnly(libs.compose.gradle.plugin)
+    compileOnly(libs.ksp.gradle.plugin)
+    compileOnly(libs.hilt.gradle.plugin)
+}
+
+gradlePlugin {
+    plugins {
+        register("androidApplication") {
+            id = "pixelwall.android.application"
+            implementationClass = "AndroidApplicationConventionPlugin"
+        }
+        register("androidLibrary") {
+            id = "pixelwall.android.library"
+            implementationClass = "AndroidLibraryConventionPlugin"
+        }
+        register("androidCompose") {
+            id = "pixelwall.android.compose"
+            implementationClass = "AndroidComposeConventionPlugin"
+        }
+        register("androidHilt") {
+            id = "pixelwall.android.hilt"
+            implementationClass = "AndroidHiltConventionPlugin"
+        }
+        register("androidFeature") {
+            id = "pixelwall.android.feature"
+            implementationClass = "AndroidFeatureConventionPlugin"
+        }
+        register("jvmLibrary") {
+            id = "pixelwall.jvm.library"
+            implementationClass = "JvmLibraryConventionPlugin"
+        }
+    }
+}