fix: apply colors via Atum template style params instead of CSS

Atum reads color values from #__template_styles params (hue, link-color,
special-color) and outputs them as inline CSS variables at render time.
Our CSS variable injection was being overridden by Atum's own output.

Now enforceAtumBranding() sets the color params directly in the DB:
- color_primary → hue (hex→HSL converted) + special-color
- color_sidebar → header-color
- color_link → link-color

Added hexToHsl() helper for the conversion. Install script also sets
default Moko theme colors at install time.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/script.php

@@ -408,6 +408,9 @@ class plgSystemMokoWaaSInstallerScript implements InstallerScriptInterface
 			'emptyLogoBrandLargeAlt' => '1',
 			'emptyLogoBrandSmallAlt' => '1',
 			'emptyLoginLogoAlt'      => '1',
+			'hue'                    => 'hsl(219, 44%, 18%)',
+			'special-color'          => '#1a2744',
+			'link-color'             => '#2ecc71',
 		];
 
 		$db    = Factory::getDbo();