Fix drag start: let startDrag() activate the automatic drag

The grip set dragProxy.Drag.active = true and then called startDrag().
For a Drag.Automatic drag that is wrong — startDrag() is what activates
the drag — so it raised "startDrag() drag must be active", the OS drag
never began, and every target showed the no-drop cursor.

Remove the manual active assignment; call startDrag() alone (it runs the
platform drag and blocks until it completes). Add Drag.proposedAction =
MoveAction. Do the drag cleanup in onReleased via commitDrop(), which
commits when the drop landed on a valid outline target and otherwise just
clears the drag state.

GUI builds clean.

ui/qml/OutlineView.qml

@@ -572,9 +572,9 @@ ListView {
                     Item {
                         id: dragProxy
                         anchors.fill: parent
-                        Drag.active: false
                         Drag.dragType: Drag.Automatic
                         Drag.supportedActions: Qt.MoveAction
+                        Drag.proposedAction: Qt.MoveAction
                         Drag.keys: ["ork-section"]
                     }
 
@@ -591,22 +591,23 @@ ListView {
                             if (started) return
                             started = true
                             // Record the drag source in the model (survives a
-                            // later file switch) and begin the OS drag.
+                            // later file switch) and begin the OS drag. For a
+                            // Drag.Automatic drag, startDrag() activates it —
+                            // do NOT set Drag.active manually first.
                             docModel.beginDrag(del.index)
                             outline.dragActive = true
                             dragProxy.Drag.mimeData = {
                                 "text/plain": docModel.dragSourceDoc()
                                               + "\t" + docModel.dragSourceId()
                             }
-                            dragProxy.Drag.active = true
                             dragProxy.Drag.startDrag()
                         }
                         onReleased: {
-                            // If the drag never produced a drop, clean up.
-                            if (outline.dragActive && !started) {
-                                outline.dragActive = false
-                                docModel.endDrag()
-                            }
+                            // startDrag() blocks until the OS drag finishes, so
+                            // by here the drop (if any) has been handled by a
+                            // DropArea. Clear any drag state that a drop didn't.
+                            if (outline.dragActive)
+                                outline.commitDrop()
                             started = false
                         }
                     }