Feature Request: Allow customization of startup pixel art

Feature Request

Description
Allow users to customize or change the pixel art (ASCII art) displayed at startup below the "Welcome back [name]!" message.

Use Case
The startup pixel art is currently a static, built-in image. It would be nice if users could personalize it — for example, by setting a custom ASCII art in a config file like ~/.claude/settings.json.

Proposed Solution
Add a setting (e.g., startupArt) in settings.json that allows users to specify custom ASCII art or choose from a set of built-in options.

Example:

{
  "startupArt": "custom"
}

Or allow a path to a custom art file:

{
  "startupArtPath": "~/.claude/startup-art.txt"
}

Thank you for considering this!