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/src/content/site.ts

@@ -0,0 +1,62 @@
+import {
+  parseAvailabilityConfig,
+  type AvailabilityConfig,
+} from "@/src/domain/availability";
+
+export const SITE_NAME = "Marc Mintel";
+export const SITE_URL = "https://mintel.me";
+
+// TODO(owner): replace with the real Cal.com link before launch.
+export const BOOKING_URL = "https://cal.com/PLACEHOLDER/intro";
+
+// TODO(owner): replace with the real contact address before launch.
+export const CONTACT_EMAIL = "hello@example.com";
+
+// PLACEHOLDER VALUES: the owner must confirm the next free date and weekly hours.
+const RAW_AVAILABILITY_CONFIG = {
+  freeFrom: "2026-11-01",
+  hoursPerWeek: 20,
+} as const;
+
+const parsedAvailability = parseAvailabilityConfig(RAW_AVAILABILITY_CONFIG);
+if (parsedAvailability.ok === false) {
+  throw new Error(
+    `Invalid AVAILABILITY_CONFIG in src/content/site.ts: ${parsedAvailability.error}`,
+  );
+}
+export const AVAILABILITY_CONFIG: AvailabilityConfig = parsedAvailability.value;
+
+export type EngagementBlock = {
+  readonly name: string;
+  readonly hoursPerWeek: string;
+  readonly pricePerMonth: string;
+};
+
+export const ENGAGEMENT_BLOCKS: readonly EngagementBlock[] = [
+  {
+    name: "Focus",
+    hoursPerWeek: "15 h/week",
+    pricePerMonth: "6,000 EUR/month",
+  },
+  {
+    name: "Half-time",
+    hoursPerWeek: "20 h/week",
+    pricePerMonth: "8,000 EUR/month",
+  },
+  {
+    name: "Full-time",
+    hoursPerWeek: "35-40 h/week",
+    pricePerMonth: "14,000-16,000 EUR/month",
+  },
+];
+
+export const STACK: readonly string[] = [
+  "TypeScript",
+  "Next.js",
+  "React",
+  "Node.js",
+  "Rust",
+  "Solidity",
+  "PostgreSQL",
+  "Tailwind CSS",
+];