feat: Add ⇧⌘T shortcut to reopen recently closed tabs

Implements a recently-closed tab stack on the Editor model. When a tab is
closed, its file reference is pushed onto the stack (up to 20 entries).
Pressing ⇧⌘T (Shift+Command+T) pops the most recently closed tab and
reopens it in the active editor.

Changes:
- Editor: Add recentlyClosedTabs stack, addToRecentlyClosed(), reopenClosedTab()
- CodeEditWindowController: Add reopenClosedTab(_:) action
- FileCommands: Add 'Reopen Closed Tab' menu item with ⇧⌘T shortcut

Closes #1656

Author: William-Laverty

CodeEdit/Features/Documents/Controllers/CodeEditWindowController.swift

@@ -198,6 +198,10 @@ final class CodeEditWindowController: NSWindowController, NSToolbarDelegate, Obs
         }
     }
 
+    @IBAction func reopenClosedTab(_ sender: Any) {
+        workspace?.editorManager?.activeEditor.reopenClosedTab()
+    }
+
     @IBAction func closeActiveEditor(_ sender: Any) {
         if workspace?.editorManager?.editorLayout.findSomeEditor(
             except: workspace?.editorManager?.activeEditor

CodeEdit/Features/Editor/Models/Editor/Editor.swift

@@ -57,6 +57,12 @@ final class Editor: ObservableObject, Identifiable {
 
     @Published var temporaryTab: Tab?
 
+    /// Stack of recently closed files, used to support reopening closed tabs via ⇧⌘T.
+    @Published var recentlyClosedTabs: [CEWorkspaceFile] = []
+
+    /// Maximum number of recently closed tabs to remember.
+    private static let maxRecentlyClosedTabs = 20
+
     var id = UUID()
 
     weak var parent: SplitViewData?
@@ -145,6 +151,9 @@ final class Editor: ObservableObject, Identifiable {
     func closeTab(file: CEWorkspaceFile, fromHistory: Bool = false) {
         guard canCloseTab(file: file) else { return }
 
+        // Remember the closed tab so it can be reopened with ⇧⌘T
+        addToRecentlyClosed(file)
+
         if temporaryTab?.file == file {
             temporaryTab = nil
         }
@@ -322,6 +331,29 @@ final class Editor: ObservableObject, Identifiable {
 
     /// Remove the given file from tabs.
     /// - Parameter file: The file to remove.
+        // MARK: - Recently Closed Tabs
+
+    /// Pushes a file onto the recently-closed stack.
+    private func addToRecentlyClosed(_ file: CEWorkspaceFile) {
+        // Remove duplicates so the most recent close is always on top
+        recentlyClosedTabs.removeAll(where: { $0 == file })
+        recentlyClosedTabs.append(file)
+        if recentlyClosedTabs.count > Self.maxRecentlyClosedTabs {
+            recentlyClosedTabs.removeFirst()
+        }
+    }
+
+    /// Reopens the most recently closed tab, if any.
+    func reopenClosedTab() {
+        guard let file = recentlyClosedTabs.popLast() else { return }
+        openTab(file: file)
+    }
+
+    /// Whether there are any recently closed tabs that can be reopened.
+    var canReopenClosedTab: Bool {
+        !recentlyClosedTabs.isEmpty
+    }
+
     func removeTab(_ file: CEWorkspaceFile) {
         tabs.removeAll(where: { tab in tab.file == file })
         if temporaryTab?.file == file {

CodeEdit/Features/WindowCommands/FileCommands.swift

@@ -51,6 +51,13 @@ struct FileCommands: Commands {
             }
             .keyboardShortcut("w")
 
+            Button("Reopen Closed Tab") {
+                NSApp.sendAction(#selector(CodeEditWindowController.reopenClosedTab(_:)), to: nil, from: nil)
+            }
+            .keyboardShortcut("t", modifiers: [.shift, .command])
+
+            Divider()
+
             Button("Close Editor") {
                 if NSApp.target(forAction: #selector(CodeEditWindowController.closeActiveEditor(_:))) != nil {
                     NSApp.sendAction(