feat: Add ⇧⌘T shortcut to reopen closed tabs

Implements #1656

This PR adds the ability to reopen recently closed editor tabs using the
⇧⌘T (Shift+Command+T) keyboard shortcut, a common convention in most
editors and browsers.

Changes:
- Add closedTabsHistory to Editor to track recently closed tabs (up to 20)
- Modify closeTab() to save tabs to the closed history before closing
- Add reopenLastClosedTab() method to Editor
- Add reopenClosedTab action to CodeEditWindowController
- Add 'Reopen Closed Tab' menu item to File menu with ⇧⌘T shortcut

The history is per-editor, so each split view maintains its own closed
tab history. Users can repeatedly press ⇧⌘T to reopen multiple tabs
in the order they were closed.

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.reopenLastClosedTab()
+    }
+
     @IBAction func closeActiveEditor(_ sender: Any) {
         if workspace?.editorManager?.editorLayout.findSomeEditor(
             except: workspace?.editorManager?.activeEditor

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

@@ -52,6 +52,13 @@ final class Editor: ObservableObject, Identifiable {
     /// - Warning: Use the ``addToHistory(_:)`` or ``clearFuture()`` methods to modify this. Do not modify directly.
     @Published var history: Deque<CEWorkspaceFile> = []
 
+    /// Maintains the list of recently closed tabs that can be reopened.
+    /// The most recently closed tab is at the front of the deque.
+    @Published var closedTabsHistory: Deque<CEWorkspaceFile> = []
+
+    /// Maximum number of closed tabs to remember.
+    private static let maxClosedTabsHistory = 20
+
     /// Currently selected tab.
     @Published private(set) var selectedTab: Tab?
 
@@ -154,6 +161,10 @@ final class Editor: ObservableObject, Identifiable {
         if file != selectedTab?.file {
             addToHistory(EditorInstance(workspace: workspace, file: file))
         }
+
+        // Add to closed tabs history for reopening later
+        addToClosedTabsHistory(file)
+
         removeTab(file)
         if let selectedTab {
             addToHistory(selectedTab)
@@ -167,6 +178,45 @@ final class Editor: ObservableObject, Identifiable {
         file.fileDocument = nil
     }
 
+    /// Adds a file to the closed tabs history.
+    /// - Parameter file: The file to add to the history.
+    private func addToClosedTabsHistory(_ file: CEWorkspaceFile) {
+        // Don't add duplicates (in case the same file is closed multiple times)
+        closedTabsHistory.removeAll(where: { $0 == file })
+
+        // Add to the front of the history
+        closedTabsHistory.prepend(file)
+
+        // Trim to max size
+        while closedTabsHistory.count > Self.maxClosedTabsHistory {
+            closedTabsHistory.removeLast()
+        }
+    }
+
+    /// Whether there are closed tabs that can be reopened.
+    var canReopenClosedTab: Bool {
+        !closedTabsHistory.isEmpty
+    }
+
+    /// Reopens the most recently closed tab.
+    /// - Returns: The file that was reopened, or nil if there are no closed tabs.
+    @discardableResult
+    func reopenLastClosedTab() -> CEWorkspaceFile? {
+        guard let file = closedTabsHistory.popFirst() else {
+            return nil
+        }
+
+        // Only reopen if the tab isn't already open
+        if !tabs.contains(where: { $0.file == file }) {
+            openTab(file: file)
+        } else {
+            // If already open, just select it
+            setSelectedTab(file)
+        }
+
+        return file
+    }
+
     /// Closes the currently opened tab in the tab group.
     func closeSelectedTab() {
         guard let file = selectedTab?.file else {

CodeEdit/Features/WindowCommands/FileCommands.swift

@@ -51,6 +51,11 @@ struct FileCommands: Commands {
             }
             .keyboardShortcut("w")
 
+            Button("Reopen Closed Tab") {
+                NSApp.sendAction(#selector(CodeEditWindowController.reopenClosedTab(_:)), to: nil, from: nil)
+            }
+            .keyboardShortcut("t", modifiers: [.command, .shift])
+
             Button("Close Editor") {
                 if NSApp.target(forAction: #selector(CodeEditWindowController.closeActiveEditor(_:))) != nil {
                     NSApp.sendAction(