Fix clearScreen/clearScrollback for split panes and update all help text

- Fixed Cmd+K crash by handling both tab and split pane modes
- Updated startup message to show Cmd+I for AI (not Cmd+K)
- clearScreen and clearScrollback now work with active pane
- All documentation now consistent with correct shortcuts

MainWindowController.swift

@@ -533,25 +533,39 @@ class MainWindowController: NSWindowController {
     }
     
     @objc func clearScreen() {
-        if let session = tabManager.getCurrentSession() {
+        // If in split pane mode, clear the active pane
+        if panes.count > 0 && activePaneIndex < panes.count {
+            let session = panes[activePaneIndex]
+            session.textView.string = ""
+            session.showPrompt()
+        } else if let session = tabManager.getCurrentSession() {
+            // Otherwise clear the current tab
             session.textView.string = ""
             session.showPrompt()
         }
     }
     
     @objc func clearScrollback() {
-        if let session = tabManager.getCurrentSession() {
-            let alert = NSAlert()
-            alert.messageText = "Clear Scrollback?"
-            alert.informativeText = "This will clear all terminal output history."
-            alert.addButton(withTitle: "Clear")
-            alert.addButton(withTitle: "Cancel")
-            alert.alertStyle = .warning
-            
-            if alert.runModal() == .alertFirstButtonReturn {
-                session.textView.string = ""
-                session.showPrompt()
-            }
+        // Get the active session (either from pane or tab)
+        let session: TerminalSession?
+        if panes.count > 0 && activePaneIndex < panes.count {
+            session = panes[activePaneIndex]
+        } else {
+            session = tabManager.getCurrentSession()
+        }
+        
+        guard let activeSession = session else { return }
+        
+        let alert = NSAlert()
+        alert.messageText = "Clear Scrollback?"
+        alert.informativeText = "This will clear all terminal output history."
+        alert.addButton(withTitle: "Clear")
+        alert.addButton(withTitle: "Cancel")
+        alert.alertStyle = .warning
+        
+        if alert.runModal() == .alertFirstButtonReturn {
+            activeSession.textView.string = ""
+            activeSession.showPrompt()
         }
     }