Cleaned up logic within ImageRepo

- Moved out extension check to ImageService as that seems more relevant.
- Updated models to use static-style references instead of facade to align with common modern usage within the app.
- Updated custom image_extension validation rule to use shared logic in image service.

app/Entities/Tools/PageContent.php

@@ -9,6 +9,7 @@ use BookStack\Exceptions\ImageUploadException;
 use BookStack\Facades\Theme;
 use BookStack\Theming\ThemeEvents;
 use BookStack\Uploads\ImageRepo;
+use BookStack\Uploads\ImageService;
 use BookStack\Util\HtmlContentFilter;
 use DOMDocument;
 use DOMNodeList;
@@ -130,7 +131,7 @@ class PageContent
         $imageInfo = $this->parseBase64ImageUri($uri);
 
         // Validate extension and content
-        if (empty($imageInfo['data']) || !$imageRepo->imageExtensionSupported($imageInfo['extension'])) {
+        if (empty($imageInfo['data']) || !ImageService::isExtensionSupported($imageInfo['extension'])) {
             return '';
         }