Add ESLint and Prettier

Prettier owns formatting: .prettierrc.json, format and format:check scripts, and
a one-off pass over the repo so the check is green from the start. Embedded
language formatting is off deliberately - the renderers build HTML in html
tagged templates and letting Prettier reflow those would change the markup
customers receive. docs/ is excluded because it is hand-wrapped prose, and shell
scripts have no Prettier parser.

ESLint covers the JavaScript: the two browser scripts, the build and check
scripts, and its own config. no-var is scoped out for the browser scripts on
purpose; they are plain ES5-shaped IIFEs and a hoisting difference would only
show up in a browser.

ESLint cannot lint the TypeScript here: typescript@7 is the native port with no
JavaScript compiler API, and typescript-eslint requires a 4.8-6.1 peer, so it
refuses to install and forcing it through would leave a parser that cannot read
the compiler. tsc --noEmit stays the TypeScript gate; README records the two
ways to change that.

lint and format:check now run in deploy.sh, and VS Code formats on save with
Prettier and surfaces ESLint findings.

test/config.test.ts

@@ -33,7 +33,9 @@ describe('parseSiteConfig', () => {
     const config = parseSiteConfig(
       minimal({
         theme: { copper: '#b2703b' },
-        sections: [{ slug: 'wine', label: 'Wine', shortLabel: 'Wine', note: 'By the glass', order: 1 }],
+        sections: [
+          { slug: 'wine', label: 'Wine', shortLabel: 'Wine', note: 'By the glass', order: 1 },
+        ],
       }),
     );
     assert.equal(config.theme.copper, '#b2703b');
@@ -77,7 +79,8 @@ describe('parseSiteConfig', () => {
 
   it('rejects a malformed slug', () => {
     assert.throws(
-      () => parseSiteConfig(minimal({ sections: [{ slug: 'Straight Drinks', label: 'x', order: 1 }] })),
+      () =>
+        parseSiteConfig(minimal({ sections: [{ slug: 'Straight Drinks', label: 'x', order: 1 }] })),
       ConfigError,
     );
   });