Scalar Presence: brand-panel login (light/dark), Poppins, splash and launcher icons, fixed API base via dart-define, keep-signed-in, Android project

- Login reworked to the Brand panel layout with a dark-theme switch; 'Scalar Presence' two-line wordmark
- Android project now tracked (was gitignored); pins shared_preferences_android 2.4.27 (2.5.0 crashed with a black screen)
- API base URL fixed per build (--dart-define=API_BASE_URL), no in-app server setting

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

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")