Redesign the calculator as a hotel at night

[alihdrndm]

What

The browser calculator now looks like it belongs to its subject instead of a plain form.

• The block as a hotel at night. One tower per night, one window per room: amber for booked, coral for rooms short of that night's minimum, outlined for rooms the hotel resold, dark for rooms allowed to stay empty, and a mint line at the minimum. Big blocks scale to a few rooms per window, with a note. It has a text alternative for screen readers and a night-by-night table.
• The two bills as hotel folios, side by side, with the per-night bill itemising each short night and the higher one stamped.
• Live results. It recalculates on every keystroke and opens on the worked example, so the first view is a real block.
• Bundled font (Bricolage Grotesque via Fontsource), so the page still makes no third-party requests.

Fix

Changing the number of nights and then clicking into a night used to rebuild the table on blur and drop what you typed. The table is now only rebuilt when the dates change.

Checks

• Lint, typecheck, the 5 calculator tests and the build pass.
• Checked in a browser at 1440 px and 390 px: no horizontal scroll on the phone, worked example still gives $975.60 and $1,528.80, resell credit, a 12-night block with a 250-room night, and an invalid currency.