feat: add RRULE parsing to shared package and improve ProposedEventCard UI

- Add rrule library to shared package for RRULE string parsing
- Add rruleHelpers.ts with parseRRule() returning freq, until, count, interval, byDay
- Add formatters.ts with German date/time formatters for client and server
- Extend CreateEventDTO with exceptionDates field for proposals
- Extend ChatModel schema with exceptionDates, deleteMode, occurrenceDate
- Update proposeUpdateEvent tool to support isRecurring and recurrenceRule params
- ProposedEventCard now shows green "Neue Ausnahme" and "Neues Ende" text
- Add Sport test scenario with dynamic exception and UNTIL responses
- Update CLAUDE.md documentation

packages/shared/src/models/CalendarEvent.ts

@@ -28,6 +28,7 @@ export interface CreateEventDTO {
   note?: string;
   isRecurring?: boolean;
   recurrenceRule?: string;
+  exceptionDates?: string[]; // For display in proposals
 }
 
 export interface UpdateEventDTO {

packages/shared/src/utils/formatters.ts

@@ -0,0 +1,48 @@
+/**
+ * German date/time formatting helpers.
+ * Used across client and server.
+ */
+
+/**
+ * Format date as DD.MM.YYYY
+ */
+export function formatDate(date: Date): string {
+  const d = new Date(date);
+  return d.toLocaleDateString("de-DE", {
+    day: "2-digit",
+    month: "2-digit",
+    year: "numeric",
+  });
+}
+
+/**
+ * Format time as HH:MM
+ */
+export function formatTime(date: Date): string {
+  const d = new Date(date);
+  return d.toLocaleTimeString("de-DE", {
+    hour: "2-digit",
+    minute: "2-digit",
+  });
+}
+
+/**
+ * Format date and time as DD.MM.YYYY HH:MM:SS
+ */
+export function formatDateTime(date: Date): string {
+  const d = new Date(date);
+  return `${formatDate(d)} ${d.toLocaleTimeString("de-DE")}`;
+}
+
+/**
+ * Format date with weekday as "Mo., DD.MM.YYYY"
+ */
+export function formatDateWithWeekday(date: Date): string {
+  const d = new Date(date);
+  return d.toLocaleDateString("de-DE", {
+    weekday: "short",
+    day: "2-digit",
+    month: "2-digit",
+    year: "numeric",
+  });
+}

packages/shared/src/utils/index.ts

@@ -1 +1,3 @@
 export * from "./dateHelpers";
+export * from "./rruleHelpers";
+export * from "./formatters";

packages/shared/src/utils/rruleHelpers.ts

@@ -0,0 +1,49 @@
+import { rrulestr, Frequency } from "rrule";
+
+export interface ParsedRRule {
+  freq: string; // "YEARLY", "MONTHLY", "WEEKLY", "DAILY", etc.
+  until?: Date;
+  count?: number;
+  interval?: number;
+  byDay?: string[]; // ["MO", "WE", "FR"]
+}
+
+const FREQ_NAMES: Record<Frequency, string> = {
+  [Frequency.YEARLY]: "YEARLY",
+  [Frequency.MONTHLY]: "MONTHLY",
+  [Frequency.WEEKLY]: "WEEKLY",
+  [Frequency.DAILY]: "DAILY",
+  [Frequency.HOURLY]: "HOURLY",
+  [Frequency.MINUTELY]: "MINUTELY",
+  [Frequency.SECONDLY]: "SECONDLY",
+};
+
+/**
+ * Parses an RRULE string and extracts the relevant fields.
+ * Handles both with and without "RRULE:" prefix.
+ */
+export function parseRRule(ruleString: string): ParsedRRule | null {
+  if (!ruleString) {
+    return null;
+  }
+
+  try {
+    // Ensure RRULE: prefix is present
+    const normalized = ruleString.startsWith("RRULE:")
+      ? ruleString
+      : `RRULE:${ruleString}`;
+
+    const rule = rrulestr(normalized);
+    const options = rule.options;
+
+    return {
+      freq: FREQ_NAMES[options.freq] || "UNKNOWN",
+      until: options.until || undefined,
+      count: options.count || undefined,
+      interval: options.interval > 1 ? options.interval : undefined,
+      byDay: options.byweekday?.map((d) => d.toString()) || undefined,
+    };
+  } catch {
+    return null;
+  }
+}