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/app/(tabs)/chat.tsx

@@ -9,7 +9,7 @@ import {
 } from "react-native";
 import { useThemeStore } from "../../stores/ThemeStore";
 import React, { useState, useRef, useEffect, useCallback } from "react";
-import { useFocusEffect } from "expo-router";
+import { useFocusEffect, router } from "expo-router";
 import Header from "../../components/Header";
 import BaseBackground from "../../components/BaseBackground";
 import { FlashList } from "@shopify/flash-list";
@@ -38,6 +38,7 @@ type ChatMessageProps = {
   proposedChanges?: ProposedEventChange[];
   onConfirm?: (proposalId: string, proposal: ProposedEventChange) => void;
   onReject?: (proposalId: string) => void;
+  onEdit?: (proposalId: string, proposal: ProposedEventChange) => void;
 };
 
 type ChatInputProps = {
@@ -62,6 +63,7 @@ const Chat = () => {
   const [currentConversationId, setCurrentConversationId] = useState<
     string | undefined
   >();
+  const [hasLoadedMessages, setHasLoadedMessages] = useState(false);
 
   useEffect(() => {
     const keyboardDidShow = Keyboard.addListener(
@@ -71,10 +73,11 @@ const Chat = () => {
     return () => keyboardDidShow.remove();
   }, []);
 
-  // Load existing messages from database once authenticated and screen is focused
+  // Load existing messages from database only once (on initial mount)
+  // Skip on subsequent focus events to preserve local edits (e.g., edited proposals)
   useFocusEffect(
     useCallback(() => {
-      if (isAuthLoading || !isAuthenticated) return;
+      if (isAuthLoading || !isAuthenticated || hasLoadedMessages) return;
 
       const fetchMessages = async () => {
         try {
@@ -91,10 +94,12 @@ const Chat = () => {
           }
         } catch (error) {
           console.error("Failed to load messages:", error);
+        } finally {
+          setHasLoadedMessages(true);
         }
       };
       fetchMessages();
-    }, [isAuthLoading, isAuthenticated]),
+    }, [isAuthLoading, isAuthenticated, hasLoadedMessages]),
   );
 
   const scrollToEnd = () => {
@@ -159,6 +164,22 @@ const Chat = () => {
     }
   };
 
+  const handleEditProposal = (
+    messageId: string,
+    conversationId: string,
+    proposalId: string,
+    proposal: ProposedEventChange,
+  ) => {
+    router.push({
+      pathname: "/editEvent",
+      params: {
+        mode: "chat",
+        eventData: JSON.stringify(proposal.event),
+        proposalContext: JSON.stringify({ messageId, proposalId, conversationId }),
+      },
+    });
+  };
+
   const handleSend = async (text: string) => {
     // Show user message immediately
     const userMessage: MessageData = {
@@ -238,6 +259,14 @@ const Chat = () => {
                   proposalId,
                 )
               }
+              onEdit={(proposalId, proposal) =>
+                handleEditProposal(
+                  item.id,
+                  item.conversationId!,
+                  proposalId,
+                  proposal,
+                )
+              }
             />
           )}
           keyExtractor={(item) => item.id}
@@ -334,6 +363,7 @@ const ChatMessage = ({
   proposedChanges,
   onConfirm,
   onReject,
+  onEdit,
 }: ChatMessageProps) => {
   const { theme } = useThemeStore();
   const [currentIndex, setCurrentIndex] = useState(0);
@@ -361,7 +391,7 @@ const ChatMessage = ({
         {content}
       </Text>
 
-      {hasProposals && currentProposal && onConfirm && onReject && (
+      {hasProposals && currentProposal && onConfirm && onReject && onEdit && (
         <View>
           {/* Event card with optional navigation arrows */}
           <View className="flex-row items-center">
@@ -381,8 +411,9 @@ const ChatMessage = ({
             <View className="flex-1">
               <ProposedEventCard
                 proposedChange={currentProposal}
-                onConfirm={() => onConfirm(currentProposal.id, currentProposal)}
+                onConfirm={(proposal) => onConfirm(proposal.id, proposal)}
                 onReject={() => onReject(currentProposal.id)}
+                onEdit={(proposal) => onEdit(proposal.id, proposal)}
               />
             </View>