Allow customizing Companion (buddy) name

Feature Request

Allow users to configure the Companion name (the small character that sits beside the input box) via ~/.claude/settings.json or similar config.

Current behavior: The companion is hardcoded as "Quillum" (a penguin). There's no way to change the name or character.

Desired behavior: A setting like companionName in settings.json that lets users personalize the buddy name. For example:

{
  "companion": {
    "name": "Nandhi",
    "title": "Shiva's Vahana"
  }
}

Why: The companion is a delightful feature — letting users personalize it would make the experience feel more like their own.