refactor: rename package scope from @caldav to @calchat

Rename all workspace packages to reflect the actual project name:
- @caldav/client -> @calchat/client
- @caldav/server -> @calchat/server
- @caldav/shared -> @calchat/shared
- Root package: caldav-mono -> calchat-mono

Update all import statements across client and server to use the new
package names. Update default MongoDB database name and logging service
identifier accordingly.

apps/client/src/app/(tabs)/calendar.tsx

@@ -7,7 +7,7 @@ import {
   ScrollView,
   Alert,
 } from "react-native";
-import { DAYS, MONTHS, Month, ExpandedEvent } from "@caldav/shared";
+import { DAYS, MONTHS, Month, ExpandedEvent } from "@calchat/shared";
 import Header from "../../components/Header";
 import { EventCard } from "../../components/EventCard";
 import React, {