Allow customizing spinner "thinking" verbs — static list and dynamic sources

What

Let users customize the randomized thinking verbs the spinner shows while Claude works (e.g. "Coreographing…", "Shenaniganing…", "Noodling…"). Today there is no way to influence them — spinnerTipsEnabled only controls tip text and prefersReducedMotion disables the animation entirely.

Why

The verbs are a beloved part of the CLI's personality. Letting users add their own — or pull team/project/seasonal-themed ones — makes it more fun and personal. A dynamic source also lets teams share a curated set, or rotate them without editing config.

Proposed

Support multiple source types via settings.json, with a mode to either append to or replace the built-in list:

1. Static list — inline in settings:

{ "spinnerWords": { "mode": "append", "words": ["Vibing", "Percolating", "Conjuring"] } }

1. Local file — path to a newline- or JSON-delimited word list, re-read on change:

{ "spinnerWords": { "mode": "replace", "file": "~/.claude/spinner-words.txt" } }

1. Command — like statusLine, run a script whose stdout is the word list (enables server/API fetch, caching, per-repo logic):

{ "spinnerWords": { "mode": "append", "command": "curl -s https://example.com/spinner-words" } }

All sources fall back to the built-in defaults when unset, empty, or on error (so a failed fetch never leaves the spinner blank).