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/logging/logger.ts

@@ -32,7 +32,7 @@ export const logger = pino({
       }
     : undefined,
   base: {
-    service: "caldav-server",
+    service: "calchat-server",
   },
 });