implement chat messaging with event proposals

- Add functional chat with server communication and test responses
- Add ProposedEventCard component for confirm/reject actions
- Move Constants (Day, Month) from client to shared package
- Add dateHelpers utility for weekday calculations
- Extend Themes.tsx with button and text colors
- Update CLAUDE.md with current implementation status
- Add *.tsbuildinfo to .gitignore

apps/client/src/components/ProposedEventCard.tsx

@@ -0,0 +1,86 @@
+import { View, Text, Pressable } from "react-native";
+import { ProposedEventChange } from "@caldav/shared";
+import currentTheme from "../Themes";
+
+type ProposedEventCardProps = {
+  proposedChange: ProposedEventChange;
+  respondedAction?: "confirm" | "reject";
+  onConfirm: () => void;
+  onReject: () => void;
+};
+
+function formatDateTime(date?: Date): string {
+  if (!date) return "";
+  const d = new Date(date);
+  return d.toLocaleDateString("de-DE", {
+    weekday: "long",
+    day: "2-digit",
+    month: "2-digit",
+    hour: "2-digit",
+    minute: "2-digit",
+  });
+}
+
+export const ProposedEventCard = ({
+  proposedChange,
+  respondedAction,
+  onConfirm,
+  onReject,
+}: ProposedEventCardProps) => {
+  const event = proposedChange.event;
+  const isDisabled = !!respondedAction;
+
+  return (
+    <View
+      className="border-t p-2 mt-2"
+      style={{ borderTopColor: currentTheme.placeholderBg }}
+    >
+      {/* Event Details */}
+      <Text className="font-bold text-base">{event?.title}</Text>
+      <Text style={{ color: currentTheme.textSecondary }}>
+        {formatDateTime(event?.startTime)}
+      </Text>
+      {event?.isRecurring && (
+        <Text style={{ color: currentTheme.textMuted }} className="text-sm">
+          Wiederkehrend
+        </Text>
+      )}
+
+      {/* Buttons */}
+      <View className="flex-row mt-3 gap-2">
+        <Pressable
+          onPress={onConfirm}
+          disabled={isDisabled}
+          className="flex-1 py-2 rounded-lg items-center"
+          style={{
+            backgroundColor: isDisabled
+              ? currentTheme.disabledButton
+              : currentTheme.confirmButton,
+            borderWidth: respondedAction === "confirm" ? 2 : 0,
+            borderColor: currentTheme.confirmButton,
+          }}
+        >
+          <Text style={{ color: currentTheme.buttonText }} className="font-medium">
+            Annehmen
+          </Text>
+        </Pressable>
+        <Pressable
+          onPress={onReject}
+          disabled={isDisabled}
+          className="flex-1 py-2 rounded-lg items-center"
+          style={{
+            backgroundColor: isDisabled
+              ? currentTheme.disabledButton
+              : currentTheme.rejectButton,
+            borderWidth: respondedAction === "reject" ? 2 : 0,
+            borderColor: currentTheme.rejectButton,
+          }}
+        >
+          <Text style={{ color: currentTheme.buttonText }} className="font-medium">
+            Ablehnen
+          </Text>
+        </Pressable>
+      </View>
+    </View>
+  );
+};