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/stores/ChatStore.ts

@@ -1,5 +1,5 @@
 import { create } from "zustand";
-import { ChatMessage, ProposedEventChange } from "@caldav/shared";
+import { ChatMessage, ProposedEventChange } from "@calchat/shared";
 
 type BubbleSide = "left" | "right";