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/server/src/services/interfaces/AIProvider.ts

@@ -2,7 +2,7 @@ import {
   CalendarEvent,
   ChatMessage,
   ProposedEventChange,
-} from "@caldav/shared";
+} from "@calchat/shared";
 
 export interface AIContext {
   userId: string;