feat: contrast levels and custom color picker in appearance menu

Generate medium/high contrast schemes, add a custom swatch that builds a scheme
in the browser via lazy-loaded scheme.js, allow Theme Builder exports as palettes.
Drop the teal palette and spread the swatches across the menu width.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tools/palettes/package.json

@@ -3,7 +3,7 @@
   "private": true,
   "type": "module",
   "scripts": {
-    "build": "esbuild build_palettes.mjs --bundle --platform=node --format=esm --outfile=.build/palettes.mjs --log-level=warning && node .build/palettes.mjs"
+    "build": "esbuild scheme.mjs --bundle --minify --format=iife --global-name=tonalmineScheme --outfile=../../tonalmine/javascripts/scheme.js --log-level=warning && esbuild build_palettes.mjs --bundle --platform=node --format=esm --outfile=.build/palettes.mjs --log-level=warning && node .build/palettes.mjs"
   },
   "devDependencies": {
     "@material/material-color-utilities": "0.4.0",