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>

components/offerte/form-context.tsx

@@ -0,0 +1,76 @@
+"use client";
+
+import {
+  createContext,
+  useContext,
+  useState,
+  useCallback,
+  type ReactNode,
+} from "react";
+import type { QuoteData } from "@/lib/validators";
+
+const TOTAL_STEPS = 5; // 4 form steps + 1 summary
+
+type FormData = Partial<QuoteData>;
+
+interface FormContextValue {
+  currentStep: number;
+  formData: FormData;
+  totalSteps: number;
+  nextStep: () => void;
+  prevStep: () => void;
+  goToStep: (step: number) => void;
+  updateData: (data: Partial<FormData>) => void;
+  reset: () => void;
+}
+
+const FormContext = createContext<FormContextValue | null>(null);
+
+export function FormProvider({ children }: { children: ReactNode }) {
+  const [currentStep, setCurrentStep] = useState(0);
+  const [formData, setFormData] = useState<FormData>({});
+
+  const nextStep = useCallback(() => {
+    setCurrentStep((s) => Math.min(s + 1, TOTAL_STEPS - 1));
+  }, []);
+
+  const prevStep = useCallback(() => {
+    setCurrentStep((s) => Math.max(s - 1, 0));
+  }, []);
+
+  const goToStep = useCallback((step: number) => {
+    setCurrentStep(Math.max(0, Math.min(step, TOTAL_STEPS - 1)));
+  }, []);
+
+  const updateData = useCallback((data: Partial<FormData>) => {
+    setFormData((prev) => ({ ...prev, ...data }));
+  }, []);
+
+  const reset = useCallback(() => {
+    setCurrentStep(0);
+    setFormData({});
+  }, []);
+
+  return (
+    <FormContext.Provider
+      value={{
+        currentStep,
+        formData,
+        totalSteps: TOTAL_STEPS,
+        nextStep,
+        prevStep,
+        goToStep,
+        updateData,
+        reset,
+      }}
+    >
+      {children}
+    </FormContext.Provider>
+  );
+}
+
+export function useFormContext() {
+  const ctx = useContext(FormContext);
+  if (!ctx) throw new Error("useFormContext must be used within <FormProvider>");
+  return ctx;
+}