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)/chat.tsx

@@ -18,7 +18,7 @@ import {
   chatMessageToMessageData,
   MessageData,
 } from "../../stores";
-import { ProposedEventChange } from "@caldav/shared";
+import { ProposedEventChange } from "@calchat/shared";
 import { ProposedEventCard } from "../../components/ProposedEventCard";
 import { Ionicons } from "@expo/vector-icons";