fix(desktop): set macOS dock / Cmd+Tab icon via Taskbar API

Window(icon = ...) only sets the in-title-bar proxy icon — it does NOT
drive the Cmd+Tab app switcher on macOS. That reads java.awt.Taskbar's
iconImage, which was never set, so gradle-run sessions showed the
generic Java coffee-cup square.

Load the PNG via ImageIO (preserves alpha), then set Taskbar.iconImage
before the application{} block starts. Guarded by isTaskbarSupported +
Feature.ICON_IMAGE so the call is a no-op on platforms without it.

Applies on all OSes that support the Taskbar API — macOS gets the dock
icon, GNOME/KDE get the task-switcher thumbnail, Windows gets the
taskbar icon.

https://claude.ai/code/session_01NufduPfZvYQVYwLkbCjCUo

desktopApp/src/jvmMain/kotlin/com/vitorpamplona/amethyst/desktop/Main.kt

@@ -196,6 +196,26 @@ fun main() {
         System.setProperty("apple.awt.application.appearance", "system")
     }
 
+    // Set the dock / taskbar icon image before any window is shown.
+    //
+    // On macOS the Cmd+Tab app switcher and the dock use the Taskbar API's
+    // iconImage, NOT the Window(icon=) composable parameter (which only sets
+    // the in-title-bar proxy icon). Without this, a JVM launched via gradle
+    // shows the generic Java coffee-cup square in Cmd+Tab. ImageIO preserves
+    // the PNG alpha channel so the dock renders the logo with transparency.
+    try {
+        val bytes = Unit::class.java.getResourceAsStream("/icon.png")!!.readBytes()
+        val awtImage = javax.imageio.ImageIO.read(java.io.ByteArrayInputStream(bytes))
+        if (awtImage != null && java.awt.Taskbar.isTaskbarSupported()) {
+            val taskbar = java.awt.Taskbar.getTaskbar()
+            if (taskbar.isSupported(java.awt.Taskbar.Feature.ICON_IMAGE)) {
+                taskbar.iconImage = awtImage
+            }
+        }
+    } catch (e: Exception) {
+        Log.w("Main") { "Failed to set dock icon: ${e.message}" }
+    }
+
     Log.minLevel = LogLevel.DEBUG
     DesktopImageLoaderSetup.setup()
     Runtime.getRuntime().addShutdownHook(