[Feature Request] Add `shell_id` to `/bashes` all running background bash shells

## Feature Request

Currently, there's no way to list all running background bash shell ids created with run_in_background: true.

### Current Limitation

• BashOutput(bash_id) requires knowing the shell_id
• KillShell(shell_id) requires knowing the shell_id
• No tool exists to discover active shell_ids

### Proposed Solution
Add a new column shell_ids in /bashes that returns:

• shell_ids
• Their commands
• Their start times
• Their current status

### Use Case
When managing multiple background tasks (e.g., dev servers, build processes),
users need to see what's running without remembering each shell_id.

Environment Info

• Platform: darwin
• Terminal: vscode
• Version: 2.0.37
• Feedback ID: 27aa4e15-effa-46e7-bcea-5f950f5f281b