Allow customization of the companion (animal, name, personality)

Feature Request

The companion feature (currently Mosswell the turtle) is a nice touch, but it would be great to customize it.

What I'd like to change:

• Animal — e.g. swap the turtle for an elephant, dog, owl, etc.
• Name — e.g. "Marcus" instead of "Mosswell"
• Personality traits — the current wisdom/calm vibe is great, but users should be able to tune this

Suggested implementation:
A companion key in ~/.claude/settings.json:

{
  "companion": {
    "animal": "elephant",
    "name": "Marcus",
    "personality": "stoic, wise, not reckless"
  }
}

The current defaults (Mosswell the turtle) would remain for anyone who doesn't customize.

Why it matters:
The companion is a small but personal part of the experience. Letting users make it their own would make Claude Code feel more like theirs.