Add theming system with light/dark mode support and CSS variables

app/controller/_base.php

@@ -70,6 +70,11 @@ public function __construct($layout = '')
 
 			if (($theme) && (is_dir(public_path() . '/themes/' . $theme))) {
 				ThemeModule::load(public_path() . '/themes/' . $theme);
+			} else {
+				// Load default theme if no user theme is set
+				if (is_dir(public_path() . '/themes/default')) {
+					ThemeModule::load(public_path() . '/themes/default');
+				}
 			}
 		}
 	}

app/lang/en/app.php

@@ -285,6 +285,10 @@
 	'danger_count' => '{count} in danger',
 	'all_in_good_standing' => 'All fine',
 	'theme' => 'Theme',
+	'toggle_theme' => 'Toggle theme',
+	'light_mode' => 'Light Mode',
+	'dark_mode' => 'Dark Mode',
+	'auto_mode' => 'Auto Mode',
 	'themes' => 'Themes',
 	'confirm_generate_new_token' => 'Generating a new token will invalidate the previous one. Do you want to proceed?',
 	'themes_hint' => 'Here you can import themes. Select a zip-file of your theme you want to import and once import succeeded, the theme will be available to all users. Note: If the zip-archive contains multiple themes, then the system will try to import all of them.',

app/modules/ThemeModule.php

@@ -250,6 +250,63 @@ public static function getList()
         }
     }
 
+    /**
+     * Get CSS variables for theme customization
+     * @return array
+     */
+    public static function getCssVariables()
+    {
+        if (!self::ready()) {
+            return [];
+        }
+
+        $variables = [];
+
+        // Add theme-specific CSS variables if defined
+        if (isset(self::$theme_data->css_variables)) {
+            foreach (self::$theme_data->css_variables as $key => $value) {
+                $variables[$key] = $value;
+            }
+        }
+
+        return $variables;
+    }
+
+    /**
+     * Generate inline CSS for theme variables
+     * @return string
+     */
+    public static function getCssVariablesInline()
+    {
+        $variables = self::getCssVariables();
+
+        if (empty($variables)) {
+            return '';
+        }
+
+        $css = '<style id="theme-variables">:root {';
+        foreach ($variables as $key => $value) {
+            $css .= '--' . $key . ': ' . $value . ';';
+        }
+        $css .= '}</style>';
+
+        return $css;
+    }
+
+    /**
+     * Check if theme supports light/dark mode
+     * @return bool
+     */
+    public static function supportsLightDarkMode()
+    {
+        if (!self::ready()) {
+            return false;
+        }
+
+        return isset(self::$theme_data->supports_light_dark_mode) && 
+               self::$theme_data->supports_light_dark_mode === true;
+    }
+
     /**
      * @param $theme
      * @return void