feat: add EditEventScreen with calendar and chat mode support

Add a unified event editor that works in two modes:
- Calendar mode: Create/edit events directly via EventService API
- Chat mode: Edit AI-proposed events before confirming them

The chat mode allows users to modify proposed events (title, time,
recurrence) and persists changes both locally and to the server.

New components: DateTimePicker, ScrollableDropdown, useDropdownPosition
New API: PUT /api/chat/messages/:messageId/proposal

apps/client/src/components/EventCardBase.tsx

@@ -3,6 +3,12 @@ import { Feather } from "@expo/vector-icons";
 import { ReactNode } from "react";
 import { useThemeStore } from "../stores/ThemeStore";
 import { CardBase } from "./CardBase";
+import {
+  isMultiDayEvent,
+  formatDateWithWeekday,
+  formatDateWithWeekdayShort,
+  formatTime,
+} from "@calchat/shared";
 
 type EventCardBaseProps = {
   className?: string;
@@ -14,24 +20,6 @@ type EventCardBaseProps = {
   children?: ReactNode;
 };
 
-function formatDate(date: Date): string {
-  const d = new Date(date);
-  return d.toLocaleDateString("de-DE", {
-    weekday: "short",
-    day: "2-digit",
-    month: "2-digit",
-    year: "numeric",
-  });
-}
-
-function formatTime(date: Date): string {
-  const d = new Date(date);
-  return d.toLocaleTimeString("de-DE", {
-    hour: "2-digit",
-    minute: "2-digit",
-  });
-}
-
 function formatDuration(start: Date, end: Date): string {
   const startDate = new Date(start);
   const endDate = new Date(end);
@@ -62,6 +50,7 @@ export const EventCardBase = ({
   children,
 }: EventCardBaseProps) => {
   const { theme } = useThemeStore();
+  const multiDay = isMultiDayEvent(startTime, endTime);
 
   return (
     <CardBase title={title} className={className} borderWidth={2}>
@@ -73,9 +62,16 @@ export const EventCardBase = ({
           color={theme.textPrimary}
           style={{ marginRight: 8 }}
         />
-        <Text style={{ color: theme.textPrimary }}>
-          {formatDate(startTime)}
-        </Text>
+        {multiDay ? (
+          <Text style={{ color: theme.textPrimary }}>
+            {formatDateWithWeekdayShort(startTime)} →{" "}
+            {formatDateWithWeekday(endTime)}
+          </Text>
+        ) : (
+          <Text style={{ color: theme.textPrimary }}>
+            {formatDateWithWeekday(startTime)}
+          </Text>
+        )}
       </View>
 
       {/* Time with duration */}
@@ -86,10 +82,16 @@ export const EventCardBase = ({
           color={theme.textPrimary}
           style={{ marginRight: 8 }}
         />
-        <Text style={{ color: theme.textPrimary }}>
-          {formatTime(startTime)} - {formatTime(endTime)} (
-          {formatDuration(startTime, endTime)})
-        </Text>
+        {multiDay ? (
+          <Text style={{ color: theme.textPrimary }}>
+            {formatTime(startTime)} → {formatTime(endTime)}
+          </Text>
+        ) : (
+          <Text style={{ color: theme.textPrimary }}>
+            {formatTime(startTime)} - {formatTime(endTime)} (
+            {formatDuration(startTime, endTime)})
+          </Text>
+        )}
       </View>
 
       {/* Recurring indicator */}