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)

TerminalSession.swift

@@ -627,8 +627,10 @@ class TerminalSession: NSObject, NSTextViewDelegate, NSMenuDelegate {
           • Cmd+Shift+D    - Split pane horizontally (top-bottom)
           • Cmd+Shift+Enter - Zoom/unzoom active pane
           • Cmd+R          - Search command history (fuzzy search)
-          • Cmd+K          - AI command generator
+          • Cmd+I          - AI command generator
           • Cmd+P          - Command snippets
+          • Cmd+K          - Clear screen
+          • Cmd+Shift+K    - Clear scrollback
           • Cmd+,          - Settings
           • Cmd+?          - Full keyboard shortcuts reference
           • Tab            - Accept auto-suggestion