Add stopwatch to API widget type validation and defaults

The API has its own WidgetType and normalizeWidgetType that were not
updated when the stopwatch widget was added, causing 'Widget-Typ ist
ungültig' on creation.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/app/api/widgets/route.ts

@@ -2,7 +2,7 @@ import { NextRequest, NextResponse } from "next/server";
 import { requireCurrentUser, UnauthorizedError } from "@/lib/auth";
 import { prisma } from "@/lib/prisma";
 
-type WidgetType = "favorites" | "note" | "search" | "calendar" | "calculator" | "clock" | "domain-check";
+type WidgetType = "favorites" | "note" | "search" | "calendar" | "calculator" | "clock" | "domain-check" | "stopwatch";
 
 type ExistingWidgetBox = {
   x: number;
@@ -54,6 +54,11 @@ const widgetCatalog: Record<WidgetType, WidgetDefaults> = {
     title: "Domainprüfung",
     w: 16,
     h: 12
+  },
+  stopwatch: {
+    title: "Stoppuhr",
+    w: 12,
+    h: 20
   }
 };
 
@@ -65,7 +70,8 @@ function normalizeWidgetType(value: unknown): WidgetType | null {
     value === "calendar" ||
     value === "calculator" ||
     value === "clock" ||
-    value === "domain-check"
+    value === "domain-check" ||
+    value === "stopwatch"
   ) {
     return value;
   }