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/app.ts

@@ -20,7 +20,7 @@ import { logger } from "./logging";
 
 const app = express();
 const port = process.env.PORT || 3000;
-const mongoUri = process.env.MONGODB_URI || "mongodb://localhost:27017/caldav";
+const mongoUri = process.env.MONGODB_URI || "mongodb://localhost:27017/calchat";
 
 // Middleware
 app.use(express.json());