✨(front) add DavClient utility

Add DavClient utility for creating authenticated CalDAV
client instances with proper configuration.

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

src/frontend/apps/calendars/src/features/calendar/utils/DavClient.ts

@@ -0,0 +1,19 @@
+/**
+ * CalDAV client configuration utilities
+ *
+ * Provides centralized configuration for CalDAV server connections.
+ * Used by CalendarContext to initialize CalDavService.
+ */
+
+export const caldavServerUrl = `${process.env.NEXT_PUBLIC_API_ORIGIN}/api/v1.0/caldav/`;
+
+export const headers = {
+  "Content-Type": "application/xml",
+};
+
+export const fetchOptions = {
+  credentials: "include" as RequestCredentials,
+  headers: {
+    "Content-Type": "application/xml",
+  },
+};