refactor: migrate undo system from custom stacks to NSUndoManager

CHANGELOG.md

@@ -23,7 +23,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Use sheet presentation for all file open/save panels instead of free-floating dialogs
 - Replace event monitor with native SwiftUI .onKeyPress() in connection switcher
 - Extract reusable SearchFieldView component from 4 custom search field implementations
-- Replace custom resize handle with native NSSplitView for inspector panel
+
+### Changed
+
+- Migrate undo system from custom stacks to NSUndoManager — Edit menu now shows "Undo Edit Cell", "Undo Delete Row", etc.
 
 ### Added
 

TablePro/ContentView.swift

@@ -226,13 +226,7 @@ struct ContentView: View {
         } detail: {
             // MARK: - Detail (Main workspace with optional right sidebar)
             if let currentSession = currentSession, let rightPanelState, let sessionState {
-                HorizontalSplitView(
-                    isTrailingCollapsed: !rightPanelState.isPresented,
-                    trailingWidth: Bindable(rightPanelState).panelWidth,
-                    minTrailingWidth: RightPanelState.minWidth,
-                    maxTrailingWidth: RightPanelState.maxWidth,
-                    autosaveName: "InspectorSplit"
-                ) {
+                HStack(spacing: 0) {
                     MainContentView(
                         connection: currentSession.connection,
                         payload: payload,
@@ -250,15 +244,23 @@ struct ContentView: View {
                         toolbarState: sessionState.toolbarState,
                         coordinator: sessionState.coordinator
                     )
-                } trailing: {
-                    UnifiedRightPanelView(
-                        state: rightPanelState,
-                        inspectorContext: inspectorContext,
-                        connection: currentSession.connection,
-                        tables: currentSession.tables
-                    )
-                    .background(Color(nsColor: .windowBackgroundColor))
+                    .frame(maxWidth: .infinity)
+
+                    if rightPanelState.isPresented {
+                        PanelResizeHandle(panelWidth: Bindable(rightPanelState).panelWidth)
+                        Divider()
+                        UnifiedRightPanelView(
+                            state: rightPanelState,
+                            inspectorContext: inspectorContext,
+                            connection: currentSession.connection,
+                            tables: currentSession.tables
+                        )
+                        .frame(width: rightPanelState.panelWidth)
+                        .background(Color(nsColor: .windowBackgroundColor))
+                        .transition(.move(edge: .trailing))
+                    }
                 }
+                .animation(.easeInOut(duration: 0.2), value: rightPanelState.isPresented)
             } else {
                 VStack(spacing: 16) {
                     ProgressView()