Add a new token category to pharos-tokens

It is rarely necessary — most tokens fit into the five existing categories. Check with a maintainer before starting this flow.

1. Confirm it does not fit an existing category

Before creating a new category, consider:

• animation/transition → duration and easing already live in shadow.tokens.json.
• border-width → could go into radius.tokens.json (or create border.tokens.json).
• opacity → live in color.tokens.json as aliases with / (e.g. oklch(... / 0.5)).
• breakpoints → not Pharos tokens — they belong in the consumer (Tailwind config).

If after review it really does need a new category, proceed below.

2. Create the DTCG file

src/<category>.tokens.json: