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/sets.test.ts

@@ -27,10 +27,7 @@ describe('creating a Menu Set', () => {
     assert.equal(set.state, 'draft');
     assert.equal(set.manifest.publishedAt, null);
     assert.deepEqual(set.manifest.pages, []);
-    assert.equal(
-      set.dir,
-      path.join(sitePaths(dataDir).drafts, 'bar', set.manifest.id),
-    );
+    assert.equal(set.dir, path.join(sitePaths(dataDir).drafts, 'bar', set.manifest.id));
     assert.deepEqual(await filesIn(set.dir), ['manifest.json']);
 
     const listed = await store.list();
@@ -138,10 +135,7 @@ describe('publishing', () => {
 
     const published = await store.publish(set.id);
     assert.equal(published.slug, '2026-06-26');
-    assert.equal(
-      published.dir,
-      path.join(sitePaths(dataDir).published, 'bar', '2026-06-26'),
-    );
+    assert.equal(published.dir, path.join(sitePaths(dataDir).published, 'bar', '2026-06-26'));
     assert.equal(published.manifest.publishedAt, '2026-01-05T04:00:00.000Z');
     assert.deepEqual(await filesIn(sitePaths(dataDir).drafts), ['bar']);
 
@@ -169,7 +163,10 @@ describe('publishing', () => {
     await store.publish(first.id);
 
     clock.advance(60_000);
-    const second = await store.create('bar', { label: 'Bar Menu, revised', validUntil: '2026-06-26' });
+    const second = await store.create('bar', {
+      label: 'Bar Menu, revised',
+      validUntil: '2026-06-26',
+    });
     await store.addPage(second.id, { data: pngBytes('two'), originalName: 'b.jpg' });
     const published = await store.publish(second.id);
 
@@ -200,7 +197,10 @@ describe('publishing', () => {
     const page = await store.addPage(set.id, { data: pngBytes('one'), originalName: 'a.jpg' });
     await store.publish(set.id);
 
-    await assert.rejects(() => store.addPage(set.id, { data: pngBytes('two'), originalName: 'b.jpg' }), StoreError);
+    await assert.rejects(
+      () => store.addPage(set.id, { data: pngBytes('two'), originalName: 'b.jpg' }),
+      StoreError,
+    );
     await assert.rejects(() => store.update(set.id, { label: 'New' }), StoreError);
     await assert.rejects(() => store.removePage(set.id, page.id), StoreError);
   });
@@ -296,7 +296,10 @@ describe('page index', () => {
     const { store } = makeStore(dataDir);
     const draft = await store.create('bar', { label: 'Bar Menu' });
     const published = await store.create('food', { label: 'Food Menu' });
-    const draftPage = await store.addPage(draft.id, { data: pngBytes('one'), originalName: 'a.jpg' });
+    const draftPage = await store.addPage(draft.id, {
+      data: pngBytes('one'),
+      originalName: 'a.jpg',
+    });
     const publishedPage = await store.addPage(published.id, {
       data: pngBytes('two'),
       originalName: 'b.jpg',