[BUG] Do not quit on `:q` (colon q)

Environment

• Platform (select one):
• [x] Anthropic API
• [ ] AWS Bedrock
• [ ] Google Vertex AI
• [ ] Other: <!-- specify -->
• Claude CLI version: 1.0.21
• Operating System: macOS 15.5
• Terminal: Ghostty

Bug Description

I typed :q in the prompt box accidentally and was shocked to see it quit without confirmation, losing my current context.

Steps to Reproduce

1. type :q
2. press enter

Expected Behavior

I did not expect it to quit.

Actual Behavior

It quit.

Additional Context

not really.