Add module build configs and platform expect/actual stubs

- composeApp/build.gradle.kts: KMP targets (android + iOS), all dependencies
- androidApp/build.gradle.kts: Android app with compose compiler
- Platform.kt expect/actual for Android and iOS
- Android resources: launcher icons, themes, manifest

Co-Authored-By: Claude Opus 4.6 (1M context)

Signed-off-by: Avinal Kumar <avinal.xlvii@gmail.com>

androidApp/build.gradle.kts

@@ -0,0 +1,38 @@
+plugins {
+    alias(libs.plugins.android.application)
+    alias(libs.plugins.compose.multiplatform)
+    alias(libs.plugins.compose.compiler)
+}
+
+android {
+    namespace = "com.avinal.memos"
+    compileSdk = 36
+
+    defaultConfig {
+        applicationId = "com.avinal.memos"
+        minSdk = 26
+        targetSdk = 36
+        versionCode = 1
+        versionName = "1.0.0"
+    }
+
+    buildTypes {
+        release {
+            isMinifyEnabled = true
+            proguardFiles(
+                getDefaultProguardFile("proguard-android-optimize.txt"),
+                "proguard-rules.pro"
+            )
+        }
+    }
+
+    compileOptions {
+        sourceCompatibility = JavaVersion.VERSION_11
+        targetCompatibility = JavaVersion.VERSION_11
+    }
+}
+
+dependencies {
+    implementation(project(":composeApp"))
+    implementation(libs.androidx.activity.compose)
+}