Describe the bug

The CLI help text and error message for the /mode command are missing smart_approve as a valid option, even though the functionality is fully implemented and working.

To Reproduce
Steps to reproduce the behavior:

1. Run goose session
2. Type /help to see available commands
3. Observe the /mode command description shows only: ('auto', 'approve', 'chat')
4. Try an invalid mode like /mode invalid
5. See error message lists only: auto, approve, chat

Expected behavior
Both the help text and error message should include smart_approve as a valid mode option, consistent with the actual functionality and tab completion.

Screenshots
N/A

Please provide following information:

• OS & Arch: Any
• Interface: CLI
• Version: Current main branch
• Extensions enabled: N/A
• Provider & Model: N/A

Additional context
The issue is in two locations:

• crates/goose-cli/src/session/input.rs line ~245: Help text in print_help()
• crates/goose-cli/src/session/mod.rs: Error message for invalid modes

Tab completion and validation logic already correctly support smart_approve.