Enhance image rendering for clearer display

- Add `image-rendering: pixelated` to ensure sharpness of images in Chromium-based browsers

Avoid using `Sharp` service since it's not configurable. It overcompresses images, reducing their quality. Preserving image quality is essential for tutorials and especially for theme gallery.

astro.config.mjs

@@ -1,5 +1,5 @@
 // @ts-check
-import { defineConfig } from "astro/config";
+import { defineConfig, passthroughImageService } from 'astro/config';
 import starlight from "@astrojs/starlight";
 import startlightBlog from "starlight-blog";
 import starlightScrollToTop from "starlight-scroll-to-top";
@@ -100,5 +100,8 @@ export default defineConfig({
         })
       ]
     })
-  ]
+  ],
+  image: {
+    service: passthroughImageService(),
+  },
 });