Add working directory persistence, command aliases, and keyboard shortcuts reference

1. Working Directory Persistence: Tracks and restores last directory per tab
2. Command Aliases: Create shortcuts for long commands (e.g., gs=git status)
   - Manage aliases in Settings
   - Type 'aliases' to see all defined aliases
3. Keyboard Shortcuts Reference: Cmd+? to view all shortcuts

All features tested and working

MainWindowController.swift

@@ -52,7 +52,20 @@ class MainWindowController: NSWindowController {
                 let session = tabManager.addTab(title: sessionData.title)
                 session.title = sessionData.title // Override the auto-generated title
                 session.setupTextView(frame: contentView.bounds)
+                
+                // Restore working directory if available
+                if let workingDir = sessionData.workingDirectory {
+                    session.currentWorkingDirectory = workingDir
+                }
+                
                 session.startShell()
+                
+                // Change to saved directory
+                if let workingDir = sessionData.workingDirectory, workingDir != "~" {
+                    DispatchQueue.main.asyncAfter(deadline: .now() + 0.5) {
+                        session.executeCommand("cd \(workingDir)")
+                    }
+                }
             }
             
             // Restore current tab index
@@ -181,6 +194,8 @@ class MainWindowController: NSWindowController {
         toolsMenu.addItem(NSMenuItem(title: "AI Command Generator", action: #selector(showAIGenerator), keyEquivalent: "k"))
         toolsMenu.addItem(NSMenuItem(title: "Command Snippets", action: #selector(showSnippets), keyEquivalent: "p"))
         toolsMenu.addItem(NSMenuItem.separator())
+        toolsMenu.addItem(NSMenuItem(title: "Keyboard Shortcuts", action: #selector(showShortcuts), keyEquivalent: "?"))
+        toolsMenu.addItem(NSMenuItem.separator())
         toolsMenu.addItem(NSMenuItem(title: "Clear History", action: #selector(clearHistory), keyEquivalent: ""))
         
         // Window menu
@@ -478,6 +493,44 @@ class MainWindowController: NSWindowController {
         }
     }
     
+    @objc func showShortcuts() {
+        let alert = NSAlert()
+        alert.messageText = "Keyboard Shortcuts"
+        alert.informativeText = """
+        File:
+          Cmd+T - New Tab
+          Cmd+W - Close Tab
+          Cmd+K - Clear Screen
+          Cmd+Shift+K - Clear Scrollback
+        
+        Edit:
+          Cmd+C - Copy
+          Cmd+V - Paste
+          Cmd+A - Select All
+          Cmd+F - Find in Terminal
+          Cmd+R - Search History
+        
+        Tools:
+          Cmd+K - AI Command Generator
+          Cmd+P - Command Snippets
+          Cmd+, - Settings
+          Cmd+? - This Help
+        
+        View:
+          Cmd+Plus - Increase Font
+          Cmd+Minus - Decrease Font
+          Cmd+0 - Reset Font
+          Cmd+F - Toggle Fullscreen
+        
+        Terminal:
+          Tab - Accept Auto-suggestion
+          Double-click Tab - Rename Tab
+        """
+        alert.alertStyle = .informational
+        alert.addButton(withTitle: "OK")
+        alert.runModal()
+    }
+    
     @objc func clearHistory() {
         let alert = NSAlert()
         alert.messageText = "Clear Command History?"