phase-0: foundation, both apps boot end to end

Monorepo (pnpm workspaces) with two deployable apps and three pure packages.

apps/api (Hono on Node): Zod validated env that fails fast and names the problem,
Kysely factories for SQLite and Postgres chosen by DATABASE_URL scheme, portable
migrations covering the whole SPEC section 5 schema, Better Auth with the four
roles and seeded demo accounts, localized error envelope, /healthz and /readyz,
graceful SIGTERM drain. Dialect specific SQL is confined to the two factories.

apps/web (Next.js App Router): locale routed shell in es and en with a language
switcher, sign in screen, and a runtime /api proxy so the browser only ever sees
one origin and cookies stay first party.

packages/i18n ships both catalogs complete; es is generated from COPY.md and a
test re-derives it from the document on every run so it cannot drift.
packages/contracts holds the Zod schemas and the typed client the web app uses.

Verified: 43 vitest tests, 14 Playwright tests on mobile and desktop, typecheck
and lint clean, migrate and seed from a clean database, sign in through the proxy
with CSRF rejection of foreign origins.

Not verified here: docker compose. This user has no access to the docker socket.

RULES.md is absent from docs/, so packages/rules exports only RULES_VERSION and
no tax rule, check digit or deadline was invented. See DECISIONS.md.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

apps/web/app/[locale]/layout.tsx

@@ -0,0 +1,49 @@
+import { isLocale } from '@impuestos/i18n';
+import type { Metadata } from 'next';
+import { Inter } from 'next/font/google';
+import { NextIntlClientProvider } from 'next-intl';
+import { setRequestLocale } from 'next-intl/server';
+import { getT } from '@/i18n/t';
+import { notFound } from 'next/navigation';
+import type { ReactNode } from 'react';
+import { Providers } from '@/components/providers';
+import { routing } from '@/i18n/routing';
+import '../globals.css';
+
+// Self hosted by next/font: no third party font request at runtime, which keeps the
+// CSP tight (SPEC.md section 14).
+const inter = Inter({ subsets: ['latin'], variable: '--font-inter', display: 'swap' });
+
+export function generateStaticParams() {
+  return routing.locales.map((locale) => ({ locale }));
+}
+
+export async function generateMetadata(props: {
+  params: Promise<{ locale: string }>;
+}): Promise<Metadata> {
+  const { locale } = await props.params;
+  const t = await getT(locale);
+  return { title: t('common.appName') };
+}
+
+export default async function LocaleLayout({
+  children,
+  params,
+}: {
+  children: ReactNode;
+  params: Promise<{ locale: string }>;
+}) {
+  const { locale } = await params;
+  if (!isLocale(locale)) notFound();
+  setRequestLocale(locale);
+
+  return (
+    <html lang={locale} className={inter.variable} suppressHydrationWarning>
+      <body className="min-h-dvh font-sans antialiased">
+        <NextIntlClientProvider>
+          <Providers>{children}</Providers>
+        </NextIntlClientProvider>
+      </body>
+    </html>
+  );
+}