feat: add checkout summary and reservation confirmation page

checkout.js

@@ -0,0 +1,53 @@
+// Checkout & Bestätigungsseite
+
+(function () {
+  const backLink = document.getElementById("backLink");
+  const summarySection = document.getElementById("summarySection");
+  const confirmationSection = document.getElementById("confirmationSection");
+  const summaryActivity = document.getElementById("summaryActivity");
+  const summaryDate = document.getElementById("summaryDate");
+  const summaryName = document.getElementById("summaryName");
+  const activityIcon = document.getElementById("activityIcon");
+  const checkoutBtn = document.getElementById("checkoutBtn");
+
+  const selectedActivity = localStorage.getItem("selectedActivity");
+  const selectedDate = localStorage.getItem("selectedDate");
+  const selectedName = localStorage.getItem("selectedName");
+
+  if (!selectedActivity || !selectedDate || !selectedName) {
+    window.location.href = "index.html";
+    return;
+  }
+
+  summaryActivity.textContent = selectedActivity;
+  summaryName.textContent = selectedName;
+
+  const dateObj = new Date(`${selectedDate}T00:00:00`);
+  const formattedDate = dateObj.toLocaleDateString("de-DE", {
+    weekday: "long",
+    day: "numeric",
+    month: "long",
+    year: "numeric",
+  });
+  summaryDate.textContent = formattedDate;
+
+  // Icon aus appsettings.json laden, falls verfügbar
+  fetch("appsettings.json")
+    .then((res) => res.json())
+    .then((settings) => {
+      const match = (settings.activities || []).find((a) => a.name === selectedActivity);
+      if (match && match.icon) {
+        activityIcon.textContent = match.icon;
+      }
+    })
+    .catch(() => {});
+
+  checkoutBtn.addEventListener("click", () => {
+    // Später: API / Mail-Versand / Kalendereintrag ausführen
+    summarySection.classList.add("hidden");
+    if (backLink) {
+      backLink.classList.add("hidden");
+    }
+    confirmationSection.classList.remove("hidden");
+  });
+})();