[FEATURE] Feature: /rename with no argument should auto-generate session name

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

/rename requires manually typing a name. Auto-naming from the first message
often doesn't reflect what the session ended up being about.

Proposed Solution

/rename with no argument should auto-generate a descriptive name based on the
full conversation context.

• /rename → auto-generates name from conversation context
• /rename my-name → sets name manually (unchanged)

Alternative Solutions

_No response_

Priority

Low - Nice to have

Feature Category

CLI commands and flags

Use Case Example

_No response_

Additional Context

_No response_