Fix Cmd+K conflict and add custom app icon

- Changed AI Generator shortcut from Cmd+K to Cmd+I
- Cmd+K now only triggers Clear Screen
- Created custom terminal-style app icon with Python/PIL
- Updated build script to include icon in app bundle
- Updated all documentation with correct shortcuts
- New DMG with icon included (492K)

MainWindowController.swift

@@ -249,7 +249,7 @@ class MainWindowController: NSWindowController {
         let toolsMenu = NSMenu(title: "Tools")
         toolsMenuItem.submenu = toolsMenu
         
-        toolsMenu.addItem(NSMenuItem(title: "AI Command Generator", action: #selector(showAIGenerator), keyEquivalent: "k"))
+        toolsMenu.addItem(NSMenuItem(title: "AI Command Generator", action: #selector(showAIGenerator), keyEquivalent: "i"))
         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: "?"))
@@ -583,7 +583,7 @@ class MainWindowController: NSWindowController {
           Middle-click - Paste
         
         Tools:
-          Cmd+K - AI Command Generator
+          Cmd+I - AI Command Generator
           Cmd+P - Command Snippets
           Cmd+, - Settings
           Cmd+? - This Help