Update the app with some features skeleton.

Change the navigation system
Add a basic file system management to save the charactersheet.
Add a common source code directory & commonTest module.
Add test to the business class.

composeApp/build.gradle.kts

@@ -8,10 +8,10 @@ plugins {
 
 kotlin {
     jvm("desktop")
-    
+
     sourceSets {
         val desktopMain by getting
-        
+
         commonMain.dependencies {
             implementation(compose.runtime)
             implementation(compose.foundation)
@@ -21,9 +21,14 @@ kotlin {
             implementation(compose.components.uiToolingPreview)
             implementation(libs.androidx.lifecycle.viewmodel)
             implementation(libs.androidx.lifecycle.runtime.compose)
-
-            implementation("org.jetbrains.androidx.navigation:navigation-compose:2.8.0-alpha10")
+            implementation(libs.androidx.navigation.compose)
+            implementation(libs.androidx.datastore.preferences)
         }
+
+        commonTest.dependencies {
+            implementation(libs.kotlin.test)
+        }
+
         desktopMain.dependencies {
             implementation(compose.desktop.currentOs)
             implementation(libs.kotlinx.coroutines.swing)
@@ -40,6 +45,9 @@ compose.desktop {
             targetFormats(TargetFormat.Dmg, TargetFormat.Msi, TargetFormat.Deb)
             packageName = "com.pixelized.desktop.lwa"
             packageVersion = "1.0.0"
+
+            // Use system theming fot the app toolbars.
+            jvmArgs("-Dapple.awt.application.appearance=system")
         }
     }
 }