hotfix: Fix CommonJS import bug in field-based update tools

Regression from previous commit - reverted to correct CommonJS import pattern.

tsdav is a CommonJS module and requires default import + destructuring:
- import tsdavPkg from 'tsdav'
- const { updateEventFields } = tsdavPkg

Named imports fail in strict Node.js environments (Docker):
- SyntaxError: Named export 'updateEventFields' not found

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

This restores the working pattern from commit 09f4b47.

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