Clarify image processing dependency in README

Lead with Intervention Image (the library in use), note imagick as its
required underlying PHP extension rather than listing it as a first-class
requirement.

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

Author: thenickberry

README.md

@@ -22,7 +22,7 @@ CANDIDv2 is an image database application for organizing, searching, and browsin
 - PHP 8.3+
 - MariaDB 11+
 - Caddy (or any web server) + PHP-FPM
-- PHP extensions: `imagick`, `pdo_mysql`, `exif`, `zip`
+- PHP extensions: `pdo_mysql`, `exif`, `zip`, `imagick` (required by Intervention Image)
 
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