Add double-click and navigate-up callbacks to NodeEditor

BaseNode gains a double-clicked(int) callback with timer-based
detection (400ms window). NodeEditor forwards it as node-double-clicked
and adds a navigate-up callback that fires on Escape when not
creating a link.

Author: tilladam

node-editor-building-blocks.slint

@@ -339,6 +339,7 @@ export component BaseNode inherits Rectangle {
     callback pin-drag-ended(int, length, length);
     callback pin-position-changed(/* pin-id */ int, /* node-id */ int, /* pin-type */ int, /* rel-x */ length, /* rel-y */ length);
     callback clicked(int, bool);
+    callback double-clicked(int);
     callback drag-started(int, bool, length, length);
     callback drag-moved(int, length, length);
     callback drag-ended(int, length, length);
@@ -390,6 +391,13 @@ export component BaseNode inherits Rectangle {
         }
     }
 
+    // === Double-click detection ===
+    property <bool> dbl-click-armed: false;
+    dbl-click-timer := Timer {
+        interval: 400ms;
+        triggered => { root.dbl-click-armed = false; }
+    }
+
     // === Drag Handling ===
     TouchArea {
         property <bool> shift-held: false;
@@ -434,6 +442,14 @@ export component BaseNode inherits Rectangle {
                     if was-selected-on-press && !shift-held {
                         root.clicked(node-id, shift-held);
                     }
+                    // Double-click detection
+                    if root.dbl-click-armed {
+                        root.double-clicked(node-id);
+                        root.dbl-click-armed = false;
+                    } else {
+                        root.dbl-click-armed = true;
+                        dbl-click-timer.restart();
+                    }
                 }
             }
         }

node-editor.slint

@@ -222,6 +222,8 @@ export component NodeEditor {
     callback delete-selected();
     callback add-node-requested();
     callback context-menu-requested();
+    callback node-double-clicked(/* node-id */ int);
+    callback navigate-up();
     callback node-drag-started(/* node-id */ int);
     callback node-drag-ended(/* delta-x */ float, /* delta-y */ float);
 
@@ -645,6 +647,8 @@ export component NodeEditor {
             } else if event.text == Key.Escape {
                 if root.internal-is-creating-link {
                     root.cancel-link-creation();
+                } else {
+                    root.navigate-up();
                 }
                 accept
             } else if event.modifiers.control && (event.text == "n" || event.text == "N") {