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/app/(tabs)/calendar.tsx

@@ -1,5 +1,5 @@
 import { Animated, Modal, Pressable, Text, View } from "react-native";
-import { DAYS, MONTHS, Month } from "../../Constants";
+import { DAYS, MONTHS, Month } from "@caldav/shared";
 import Header from "../../components/Header";
 import React, { useEffect, useMemo, useRef, useState } from "react";
 import currentTheme from "../../Themes";