themes: tokens, house mechanics, nine themes

• web/tokens.css: the token vocabulary (and fallback values).
• web/base.css: the mechanics (press-in .btn, .panel, .chip, .field, .toggle, .stepper, .modal, .toast, .scoreboard, .cover...). Names no colour.
• web/themes/*.css: one file per look. web/index.css imports everything.
• web/theme.ts: registry, savedTheme, applyTheme, bootScript (no flash on load), FONTS_HREF.
• web/ThemePicker.tsx: swatch row.

import './kit/themes/index.css';
import { applyTheme, savedTheme } from './kit/themes/theme';
applyTheme('my-game', savedTheme('my-game'));        // namespaced so games don't share a choice

<!-- index.html <head>: paints the right theme on the first frame -->
<link href="…FONTS_HREF…" rel="stylesheet">
<script>/* paste bootScript('my-game') output */</script>

Add a look: HOW_TO_ADD_A_THEME.md.