compare.js never imported units.js, so the header unit toggle was never
built on the compare page and every temperature was stuck in °F. Import
units.js (which builds the toggle) and route the comfort target, comfort
band, and the colder/warmer/typical-miss figures through the unit
formatters, re-rendering on unit change. State stays in °F (the API's
unit); only the displayed numbers convert.
Add fmtDelta for degree *differences* (band, average miss), which scale
by 5/9 without the 32° offset that absolute temperatures use.
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