Desktop: make Ctrl+-/= zoom actually work

Two compounding bugs:
1. Nodes skipped in a plain recomposition kept their old captured
   density, so changing the zoom state left the tree unscaled — wrap the
   CompositionLocalProvider in key(zoom) to force full-tree recompose.
2. Compose focus routing missed the shortcut depending on which child
   held focus — add an AWT KeyboardFocusManager dispatcher below Compose
   (also accepts Ctrl+Up/Down, numpad +/-, Ctrl+0 reset).

User-confirmed zooming works on the live app.

app/src/main/kotlin/com/shonar/desktop/Main.kt

@@ -5,7 +5,9 @@ import androidx.compose.foundation.layout.fillMaxSize
 import androidx.compose.foundation.layout.padding
 import androidx.compose.material3.Surface
 import androidx.compose.runtime.CompositionLocalProvider
+import androidx.compose.runtime.DisposableEffect
 import androidx.compose.runtime.collectAsState
+import androidx.compose.runtime.key
 import androidx.compose.runtime.getValue
 import androidx.compose.runtime.mutableStateOf
 import androidx.compose.runtime.remember
@@ -35,6 +37,41 @@ fun main() = application {
     val screen by state.screen.collectAsState()
     // Ctrl+= / Ctrl+- zoom the whole app; Ctrl+0 resets (after a zoom).
     var zoom by remember { mutableStateOf(1f) }
+    // Belt-and-braces: Compose's focus routing can miss shortcuts depending
+    // on which child holds focus, so also hook the AWT key pipeline directly.
+    // Debug print lets us confirm from the dev log whether keys reach the JVM.
+    DisposableEffect(Unit) {
+        val mgr = java.awt.KeyboardFocusManager.getCurrentKeyboardFocusManager()
+        val disp = java.awt.KeyEventDispatcher { e ->
+            if (e.id == java.awt.event.KeyEvent.KEY_PRESSED &&
+                e.modifiers == java.awt.event.KeyEvent.CTRL_MASK
+            ) {
+                when (e.keyCode) {
+                    java.awt.event.KeyEvent.VK_EQUALS,
+                    java.awt.event.KeyEvent.VK_PLUS,
+                    java.awt.event.KeyEvent.VK_ADD,
+                    java.awt.event.KeyEvent.VK_UP -> {
+                        zoom = (zoom * 1.1f).coerceAtMost(3f)
+                        System.err.println("[zoom] ${zoom}"); true
+                    }
+                    java.awt.event.KeyEvent.VK_MINUS,
+                    java.awt.event.KeyEvent.VK_SUBTRACT,
+                    java.awt.event.KeyEvent.VK_DOWN -> {
+                        zoom = (zoom / 1.1f).coerceAtLeast(0.4f)
+                        System.err.println("[zoom] ${zoom}"); true
+                    }
+                    java.awt.event.KeyEvent.VK_0,
+                    java.awt.event.KeyEvent.VK_NUMPAD0 -> {
+                        if (zoom != 1f) { zoom = 1f; System.err.println("[zoom] reset"); true }
+                        else false
+                    }
+                    else -> false
+                }
+            } else false
+        }
+        mgr.addKeyEventDispatcher(disp)
+        onDispose { mgr.removeKeyEventDispatcher(disp) }
+    }
     Window(
         onCloseRequest = ::exitApplication,
         title = "SHONAR Desktop" + run {
@@ -56,10 +93,10 @@ fun main() = application {
                 Modifier.fillMaxSize().onPreviewKeyEvent { e ->
                     if (e.type != KeyEventType.KeyDown || !e.isCtrlPressed) return@onPreviewKeyEvent false
                     when (e.key) {
-                        Key.Equals, Key.Plus, Key.NumPadAdd -> {
+                        Key.Equals, Key.Plus, Key.NumPadAdd, Key.DirectionUp -> {
                             zoom = (zoom * 1.1f).coerceAtMost(3f); true
                         }
-                        Key.Minus, Key.NumPadSubtract -> {
+                        Key.Minus, Key.NumPadSubtract, Key.DirectionDown -> {
                             zoom = (zoom / 1.1f).coerceAtLeast(0.4f); true
                         }
                         Key.Zero, Key.NumPad0 -> {
@@ -69,6 +106,10 @@ fun main() = application {
                     }
                 },
             ) {
+                // key(zoom) forces the whole tree to recompose when zoom
+                // changes: nodes skipped in a plain recomposition keep their
+                // old captured density, which made Ctrl+-/= a no-op.
+                key(zoom) {
                 CompositionLocalProvider(
                     LocalDensity provides ScaledDensity(baseDensity, zoom),
                 ) {
@@ -84,4 +125,5 @@ fun main() = application {
                 }
             }
         }
+    }
 }