Allow customization of thinking/spinner status messages

Feature Request

What: Add a way to customize the spinner words that appear while Claude is processing (e.g., "Perambulating", "Puzzling", "Accomplishing", "Moseying", "Topsy-turvying").

Why: These messages are a fun touch, but users may want to personalize them. For example, replacing them with anime attack names, motivational quotes, or domain-specific jargon. This is a low-effort, high-delight customization.

Suggested approach: Support a config like ~/.claude/spinner-messages.json or a spinnerMessages array in ~/.claude/settings.json that overrides the default word list. If the file/config exists, randomly pick from the user's list; otherwise fall back to defaults.

Example config:

{
  "spinnerMessages": ["Rasengan", "Kamehameha", "Getsuga Tenshou", "Domain Expansion", "Bankai", "Thunder Breathing", "Detroit Smash", "Spirit Gun"]
}