Add setting to enable bypassPermissions as a selectable runtime mode

The CLI has --allow-dangerously-skip-permissions which enables bypass mode as an option without forcing it on. However, there's no equivalent setting to make this mode selectable at runtime without using the CLI flag.

Proposal: Add a setting like:

{
  "permissions": {
    "allowBypassPermissionsMode": true
  }
}

When enabled, bypassPermissions would appear as a selectable permission mode (e.g., via /permissions or a mode switcher), allowing users to toggle into it mid-session.

Why this approach:

• Safe by default - the option doesn't appear unless explicitly enabled in settings
• Mirrors the CLI behavior of --allow-dangerously-skip-permissions
• Eliminates the need for shell aliases or restarting with different flags
• Power users in trusted environments can opt-in once and have it available when needed