feat: dark theme foundation, new header/footer, shared site primitives

Adds dark design tokens, Inter + JetBrains Mono, a header with Notes,
Process, About and a Book a call button, and a footer with the availability
line driven by the tested domain core. Shared primitives live in
src/components/site, site constants in src/content/site.ts. Legacy pages
(blog, legal, contact, tags, technologies) keep a light surface via
LegacyLightSurface. Stub routes for /notes, /process and /book.

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

apps/web/app/(site)/layout.tsx

@@ -1,5 +1,5 @@
 import type { Metadata } from "next";
-import { Inter, Newsreader } from "next/font/google";
+import { Inter, JetBrains_Mono, Newsreader } from "next/font/google";
 import { Analytics } from "@/src/components/Analytics";
 import { Footer } from "@/src/components/Footer";
 import { Header } from "@/src/components/Header";
@@ -7,6 +7,11 @@ import { InteractiveElements } from "@/src/components/InteractiveElements";
 import "./globals.css";
 
 const inter = Inter({ subsets: ["latin"], variable: "--font-inter" });
+const jetbrainsMono = JetBrains_Mono({
+  subsets: ["latin"],
+  variable: "--font-jetbrains-mono",
+  display: "swap",
+});
 const newsreader = Newsreader({
   subsets: ["latin"],
   variable: "--font-newsreader",
@@ -14,14 +19,25 @@ const newsreader = Newsreader({
   display: "swap",
 });
 
+const DESCRIPTION =
+  "Senior engineer for teams that build fast with AI and don't want chaos. Strong in design and frontend, provably clean in architecture and tests. Remote, booked in weekly capacity blocks.";
+
 export const metadata: Metadata = {
   title: {
-    default: "Marc Mintel — Professionelle Websites für Unternehmen",
+    default: "Marc Mintel — Senior engineer for AI-built software",
     template: "%s | Marc Mintel",
   },
-  description:
-    "Professionelle Websites zum Fixpreis. Ein Entwickler, ein Ansprechpartner — von der Idee bis zum fertigen Ergebnis. Inklusive Sorglos-Paket: Änderungen, Wartung und Sicherheit komplett abgedeckt.",
+  description: DESCRIPTION,
   metadataBase: new URL("https://mintel.me"),
+  openGraph: {
+    type: "website",
+    siteName: "Marc Mintel",
+    title: "Marc Mintel — Senior engineer for AI-built software",
+    description: DESCRIPTION,
+    url: "https://mintel.me",
+    locale: "en_US",
+  },
+  twitter: { card: "summary_large_image" },
   icons: {
     icon: "/favicon.svg",
   },
@@ -33,8 +49,11 @@ export default function RootLayout({
   children: React.ReactNode;
 }) {
   return (
-    <html lang="de" className={`${inter.variable} ${newsreader.variable}`}>
-      <body className="min-h-screen bg-white">
+    <html
+      lang="en"
+      className={`${inter.variable} ${jetbrainsMono.variable} ${newsreader.variable}`}
+    >
+      <body className="min-h-screen bg-bg font-sans text-fg antialiased">
         <Header />
         <main>{children}</main>
         <Footer />