feat: Add Delete key and undo/redo for preview changes

- Add Delete key shortcut to remove selected elements from preview
- Make preview changes (move, resize, delete) undoable with Ctrl+Z
- Use QTextCursor with beginEditBlock/endEditBlock for undoable updates
- Add Delete Selected action to Edit menu

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/artifact_editor/gui.py

@@ -18,7 +18,7 @@ from typing import Optional
 from PyQt6.QtCore import Qt, QTimer, pyqtSignal, QThread, QRectF, QPointF, QSizeF
 from PyQt6.QtGui import (
     QFont, QColor, QAction, QKeySequence, QSyntaxHighlighter,
-    QTextCharFormat, QPainter, QPen, QBrush
+    QTextCharFormat, QPainter, QPen, QBrush, QTextCursor
 )
 from PyQt6.QtWidgets import (
     QApplication, QMainWindow, QWidget, QVBoxLayout, QHBoxLayout,
@@ -1511,6 +1511,13 @@ class ArtifactEditorWindow(QMainWindow):
         redo_action.triggered.connect(self.code_editor.redo)
         edit_menu.addAction(redo_action)
 
+        edit_menu.addSeparator()
+
+        delete_action = QAction("&Delete Selected", self)
+        delete_action.setShortcut(QKeySequence.StandardKey.Delete)
+        delete_action.triggered.connect(self._delete_selected_element)
+        edit_menu.addAction(delete_action)
+
         # Templates menu (rebuilt when format changes)
         self.templates_menu = menubar.addMenu("&Templates")
         self._rebuild_templates_menu()
@@ -2578,12 +2585,28 @@ class ArtifactEditorWindow(QMainWindow):
     def _on_svg_scene_changed(self):
         """Handle scene changes from the SVG manager (element moved, deleted, etc.)."""
         # Regenerate SVG from the scene and update code editor
-        # Block signals to prevent triggering a re-render
+        # Use undoable text replacement so Ctrl+Z works for preview changes
         new_svg = self.svg_selection.generate_svg()
+
+        # Block signals to prevent triggering a re-render loop
         self.code_editor.blockSignals(True)
-        self.code_editor.setPlainText(new_svg)
+
+        # Use QTextCursor to replace all text - this is undoable unlike setPlainText
+        cursor = self.code_editor.textCursor()
+        cursor.beginEditBlock()  # Group as single undo operation
+        cursor.select(cursor.SelectionType.Document)
+        cursor.insertText(new_svg)
+        cursor.endEditBlock()
+
         self.code_editor.blockSignals(False)
 
+    def _delete_selected_element(self):
+        """Delete the currently selected element in the SVG preview."""
+        if hasattr(self, 'svg_selection') and self.svg_selection:
+            self.svg_selection.delete_selected()
+            # Update the elements list
+            self._update_elements_list()
+
     def _on_svg_overlay_element_selected(self, element):
         """Handle element selection from overlay."""
         if element is None: