[FEATURE] Enter plan mode and start

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

If I enter /plan prompt I would expect claude to enter plan mode and begin working on the prompt. Instead it enters plan mode and ignores the prompt

Proposed Solution

/plan prompt should switch to plan mode and start planning

Alternative Solutions

_No response_

Priority

Critical - Blocking my work

Feature Category

CLI commands and flags

Use Case Example

_No response_

Additional Context

_No response_