fix: add an option to disable dynamic OG image generation (#476)

* fix: add an option to disable dynamic OG image generation

Add new `dynamicOgImage` option in the `SITE` object inside 
`src/config.ts` file to disable auto og-image generation during build.

Resolves #428

* docs: update guides for `SITE.dynamicOgImage` option

src/layouts/PostDetails.astro

@@ -24,7 +24,7 @@ const {
   title,
   author,
   description,
-  ogImage,
+  ogImage: initOgImage,
   canonicalURL,
   pubDatetime,
   modDatetime,
@@ -34,11 +34,24 @@ const {
 
 const { Content } = await render(post);
 
-const ogImageUrl = typeof ogImage === "string" ? ogImage : ogImage?.src;
-const ogUrl = new URL(
-  ogImageUrl ?? `/posts/${slugifyStr(title)}/index.png`,
-  Astro.url.origin
-).href;
+let ogImageUrl: string | undefined;
+
+// Determine OG image source
+if (typeof initOgImage === "string") {
+  ogImageUrl = initOgImage; // Remote OG image (absolute URL)
+} else if (initOgImage?.src) {
+  ogImageUrl = initOgImage.src; // Local asset
+}
+
+// Use dynamic OG image if enabled and no remote|local ogImage
+if (!ogImageUrl && SITE.dynamicOgImage) {
+  ogImageUrl = `/posts/${slugifyStr(title)}/index.png`;
+}
+
+// Resolve OG image URL (or fallback to SITE.ogImage / default `og.png`)
+const ogImage = ogImageUrl
+  ? new URL(ogImageUrl, Astro.url.origin).href
+  : undefined;
 
 const layoutProps = {
   title: `${title} | ${SITE.title}`,
@@ -47,7 +60,7 @@ const layoutProps = {
   pubDatetime,
   modDatetime,
   canonicalURL,
-  ogImage: ogUrl,
+  ogImage,
   scrollSmooth: true,
 };