Fix: Use CommonJS-compatible imports for tsdav field updaters

The previous fix using named imports (e8e9f4c) worked locally but failed
in Docker with: "Named export 'updateEventFields' not found. The requested
module 'tsdav' is a CommonJS module".

Changed from:
  import { updateEventFields as tsdavUpdateEventFields } from 'tsdav';

To:
  import tsdavPkg from 'tsdav';
  const { updateEventFields: tsdavUpdateEventFields } = tsdavPkg;

This pattern works in both ESM and CommonJS environments because it uses
the default import with destructuring, which is the recommended way to
import named exports from CommonJS modules in ESM contexts.

Affected files:
- src/tools/calendar/update-event-fields.js
- src/tools/contacts/update-contact-fields.js
- src/tools/todos/update-todo-fields.js

Author: PhilflowIO

src/tools/calendar/update-event-fields.js

@@ -2,7 +2,8 @@ import { tsdavManager } from '../../tsdav-client.js';
 import { validateInput } from '../../validation.js';
 import { formatSuccess, formatError } from '../../formatters.js';
 import { z } from 'zod';
-import { updateEventFields as tsdavUpdateEventFields } from 'tsdav';
+import tsdavPkg from 'tsdav';
+const { updateEventFields: tsdavUpdateEventFields } = tsdavPkg;
 
 /**
  * Schema for field-based event updates

src/tools/contacts/update-contact-fields.js

@@ -2,7 +2,8 @@ import { tsdavManager } from '../../tsdav-client.js';
 import { validateInput } from '../../validation.js';
 import { formatSuccess, formatError } from '../../formatters.js';
 import { z } from 'zod';
-import { updateVCardFields as tsdavUpdateVCardFields } from 'tsdav';
+import tsdavPkg from 'tsdav';
+const { updateVCardFields: tsdavUpdateVCardFields } = tsdavPkg;
 
 /**
  * Schema for field-based vCard updates

src/tools/todos/update-todo-fields.js

@@ -2,7 +2,8 @@ import { tsdavManager } from '../../tsdav-client.js';
 import { validateInput } from '../../validation.js';
 import { formatSuccess, formatError } from '../../formatters.js';
 import { z } from 'zod';
-import { updateTodoFields as tsdavUpdateTodoFields } from 'tsdav';
+import tsdavPkg from 'tsdav';
+const { updateTodoFields: tsdavUpdateTodoFields } = tsdavPkg;
 
 /**
  * Schema for field-based todo updates