[BUG] /rename usage message missing argument placeholder

Description

When running /rename without arguments, the error message shows:

Please provide a name for the session. Usage: /rename

This is unhelpful because it doesn't indicate that an argument is expected. It should show:

Please provide a name for the session. Usage: /rename <name>

(Or whatever argument placeholder convention the codebase uses.)

Steps to reproduce

1. Open a Claude Code session
2. Type /rename with no arguments
3. Observe the usage message

Expected behavior

The usage message should include the argument placeholder, e.g. Usage: /rename <name>

Actual behavior

The usage message shows Usage: /rename with no indication that an argument is needed.

Environment

• macOS
• Claude Code (latest)