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>

composeApp/src/androidMain/kotlin/com/avinal/memos/Platform.android.kt

@@ -0,0 +1,3 @@
+package com.avinal.memos
+
+actual fun getPlatformName(): String = "Android"

composeApp/src/commonMain/kotlin/com/avinal/memos/Platform.kt

@@ -0,0 +1,3 @@
+package com.avinal.memos
+
+expect fun getPlatformName(): String

composeApp/src/iosMain/kotlin/com/avinal/memos/MainViewController.kt

@@ -0,0 +1,5 @@
+package com.avinal.memos
+
+import androidx.compose.ui.window.ComposeUIViewController
+
+fun MainViewController() = ComposeUIViewController { App() }

composeApp/src/iosMain/kotlin/com/avinal/memos/Platform.ios.kt

@@ -0,0 +1,6 @@
+package com.avinal.memos
+
+import platform.UIKit.UIDevice
+
+actual fun getPlatformName(): String =
+    UIDevice.currentDevice.systemName() + " " + UIDevice.currentDevice.systemVersion