Add caldays (public holidays API for 195+ countries)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: cakbeanie

README.md

@@ -310,6 +310,7 @@ API | Description | Auth | HTTPS | CORS |
 ### Calendar
 API | Description | Auth | HTTPS | CORS |
 |:---|:---|:---|:---|:---|
+| [caldays](https://caldays.com/api) | Public holidays for 195+ countries | No | Yes | Yes |
 | [Calendarific](https://calendarific.com/) | Worldwide Holidays | `apiKey` | Yes | Unknown |
 | [Checkiday - National Holiday](https://apilayer.com/marketplace/checkiday-api) | Industry-leading holiday data with over 5,000 holidays and thousands of descriptions | `apiKey` | Yes | Unknown |
 | [Church Calendar](http://calapi.inadiutorium.cz/) | Catholic liturgical calendar | No | No | Unknown |