Feature Request: Add defaultRunInBackground setting for Bash commands

Feature Request

Add a global setting to run Bash commands in background by default.

Proposed Setting

{
  "bash": {
    "defaultRunInBackground": true
  }
}

Or as an environment variable:

{
  "env": {
    "CLAUDE_BASH_DEFAULT_BACKGROUND": "1"
  }
}

Use Case

Power users running long-running commands (builds, tests, servers) want them to automatically run in background without:

• Manually pressing Ctrl+B each time
• Asking Claude to "run in background" every session
• Waiting for commands to complete before continuing

Current Behavior

run_in_background is only available as a per-invocation parameter on the Bash tool, with no way to set a default.

Expected Behavior

When defaultRunInBackground: true is set:

• All Bash commands run in background by default
• User can monitor with /tasks
• Claude can retrieve output with TaskOutput

This would improve workflow for users who prefer async command execution.