Interactive Shell Support

[trmxvibs]

Add interactive shell support to OpenOperator.

Features:

• Persistent REPL interface
• CLI integration
• Natural language command execution
• Graceful exit handling
• Unit test coverage

[trmxvibs]

Implemented and verified.

Completed:

• InteractiveShell
• CLI integration
• Demo
• Unit tests

Feature already implemented before issue creation.

Closing.