Add premium configurator with split-screen layout

- Redesigned configurator page with split-screen interface
- Left: Large visual preview with sticky positioning
- Right: Premium white controls container with form steps
- Added complete configurator wizard (5 steps)
- Updated hero CTA to "Zelf ontwerpen"
- Configured Shadcn UI with Slate theme
- Added layout components (Navbar, Footer)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

lib/utils.ts

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+import { clsx, type ClassValue } from "clsx"
+import { twMerge } from "tailwind-merge"
+
+export function cn(...inputs: ClassValue[]) {
+  return twMerge(clsx(inputs))
+}

lib/validators.ts

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+import { z } from "zod/v4";
+
+// ── Step 1: Product ──────────────────────────────────────────────
+export const productTypes = ["Taatsdeur", "Scharnierdeur", "Vast Paneel"] as const;
+
+export const productSchema = z.object({
+  productType: z.enum(productTypes),
+});
+
+// ── Step 2: Dimensions ──────────────────────────────────────────
+export const dimensionsSchema = z.object({
+  height: z
+    .number({ error: "Vul een geldige hoogte in" })
+    .min(2000, "Minimaal 2000mm")
+    .max(3000, "Maximaal 3000mm"),
+  width: z
+    .number({ error: "Vul een geldige breedte in" })
+    .min(300, "Minimaal 300mm")
+    .max(3000, "Maximaal 3000mm"),
+});
+
+// ── Step 3: Options ─────────────────────────────────────────────
+export const glassTypes = ["Helder", "Rookglas", "Melkglas"] as const;
+export const finishTypes = ["Poedercoat Zwart", "Goud", "Brons"] as const;
+
+export const optionsSchema = z.object({
+  glassType: z.enum(glassTypes),
+  finish: z.enum(finishTypes),
+});
+
+// ── Step 4: Contact ─────────────────────────────────────────────
+export const contactSchema = z.object({
+  name: z.string().min(2, "Vul uw naam in"),
+  email: z.string().email("Vul een geldig e-mailadres in"),
+  phone: z.string().min(10, "Vul een geldig telefoonnummer in"),
+  note: z.string().optional(),
+});
+
+// ── Combined (used on final submission) ─────────────────────────
+export const quoteSchema = productSchema
+  .merge(dimensionsSchema)
+  .merge(optionsSchema)
+  .merge(contactSchema);
+
+export type QuoteData = z.infer<typeof quoteSchema>;
+
+// Per-step schemas for step-by-step validation
+export const stepSchemas = [
+  productSchema,
+  dimensionsSchema,
+  optionsSchema,
+  contactSchema,
+] as const;