fix: handle pythonvCard4 dict-format fields and missing phone numbers (#601)

Fix three related contacts bugs:
- Parse dict-format vCard fields ({value, type}) that pythonvCard4 returns,
  which previously crashed Pydantic validation expecting plain strings
- Include tel field in client output so phone numbers reach MCP tools
- Clarify addressbook parameter expects URI slug, not displayname

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

nextcloud_mcp_server/client/contacts.py

@@ -274,6 +274,7 @@ class ContactsClient(BaseNextcloudClient):
                         "nickname": contact.nickname,
                         "birthday": contact.bday,
                         "email": contact.email,
+                        "tel": contact.tel,
                     },
                     "addressdata": addressdata,
                 }