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.

compose.yaml

@@ -7,11 +7,11 @@ services:
     build: .
     image: menu-admin:dev
     ports:
-      - "3000:3000"
+      - '3000:3000'
     environment:
       MENU_ROOT: /data
       MENU_SITE_CONFIG: /etc/menu-app/site.json
-      SECURE_COOKIES: "false"
+      SECURE_COOKIES: 'false'
       LOG_LEVEL: info
     volumes:
       - ./config/hopsngrains.site.json:/etc/menu-app/site.json:ro