Add Flutter project skeleton (Android-only MVP)

Five-layer architecture per DMC_Architektur_und_Design.md: FlightControllerLink
abstraction (Mock + MSP stub), protocol-neutral mission domain layer, App-Mode
state machine with Ready-to-Fly gate, Drift persistence schema, and placeholder
UI screens wired via go_router. App icon generated from design/Y2_pink_dark.svg.
Verified with flutter analyze and flutter test.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

app/android/settings.gradle.kts

@@ -0,0 +1,26 @@
+pluginManagement {
+    val flutterSdkPath =
+        run {
+            val properties = java.util.Properties()
+            file("local.properties").inputStream().use { properties.load(it) }
+            val flutterSdkPath = properties.getProperty("flutter.sdk")
+            require(flutterSdkPath != null) { "flutter.sdk not set in local.properties" }
+            flutterSdkPath
+        }
+
+    includeBuild("$flutterSdkPath/packages/flutter_tools/gradle")
+
+    repositories {
+        google()
+        mavenCentral()
+        gradlePluginPortal()
+    }
+}
+
+plugins {
+    id("dev.flutter.flutter-plugin-loader") version "1.0.0"
+    id("com.android.application") version "9.0.1" apply false
+    id("org.jetbrains.kotlin.android") version "2.3.20" apply false
+}
+
+include(":app")