Add drag-reorder, validation, and flow-to-tool sync

List View:
- Enable drag-drop reordering of steps
- Show broken dependency warnings when reordering
- Steps with missing variable refs shown in red with tooltip

Validation:
- Parse {variable} references from prompts and code
- Track available variables at each step position
- Warn when steps reference undefined variables

Flow View Sync:
- Deleting nodes in flow view updates the tool model
- steps_deleted signal propagates changes to builder
- Both views stay in sync

Co-Authored-By: Claude Opus 4.5 <[email protected]>

src/cmdforge/gui/widgets/flow_graph.py

@@ -122,6 +122,9 @@ class FlowGraphWidget(QWidget):
     # Emitted when the flow structure changes
     flow_changed = Signal()
 
+    # Emitted when steps are deleted from flow view (list of step indices)
+    steps_deleted = Signal(list)
+
     def __init__(self, parent=None):
         super().__init__(parent)
         self._tool: Optional[Tool] = None
@@ -149,6 +152,7 @@ class FlowGraphWidget(QWidget):
 
         # Connect signals
         self._graph.node_double_clicked.connect(self._on_node_double_clicked)
+        self._graph.nodes_deleted.connect(self._on_nodes_deleted)
 
         # Add graph widget
         layout.addWidget(self._graph.widget, 1)
@@ -409,6 +413,20 @@ class FlowGraphWidget(QWidget):
             step_type = 'prompt' if isinstance(node, PromptNode) else 'code'
             self.node_double_clicked.emit(node._step_index, step_type)
 
+    def _on_nodes_deleted(self, nodes):
+        """Handle node deletion from the graph."""
+        # Collect step indices of deleted step nodes (not Input/Output nodes)
+        deleted_indices = []
+        for node in nodes:
+            if hasattr(node, '_step_index') and node._step_index >= 0:
+                deleted_indices.append(node._step_index)
+
+        if deleted_indices:
+            # Sort in reverse order so we delete from end first
+            deleted_indices.sort(reverse=True)
+            self.steps_deleted.emit(deleted_indices)
+            self.flow_changed.emit()
+
     def refresh(self):
         """Refresh the graph from current tool data."""
         self._rebuild_graph()