feat: add script to generate default blog cover image

- Introduced a new script `make-blog-cover.mjs` to create a default cover image for blog posts.
- The image is generated in PNG format with dimensions 1200x630, suitable for Open Graph.
- Utilizes the site's branding colors and logo from `public/nobat724.svg`.
- Includes custom font styling using the Vazirmatn font.
- The generated image is saved to `public/assets/images/blog-default-cover.png`.

app/globals.css

@@ -904,4 +904,75 @@ html {
 
 .hover-item-clinic:hover h3 {
   color: #f17732;
-}
+}
+/* ── محتوای مقاله (خروجی CKEditor پنل ادمین) ──────────────────────────────
+   sanitizeHtml عمداً class و style را حذف می‌کند، پس استایل جدول/لیست/تیتر
+   باید از این‌جا بیاید وگرنه محتوا لخت و بدون ساختار دیده می‌شود. */
+.blog-content h2,
+.blog-content h3,
+.blog-content h4,
+.blog-content h5 {
+  color: #3b3b3b;
+  font-weight: 700;
+  margin: 24px 0 12px;
+  line-height: 1.8;
+}
+.blog-content h2 { font-size: 20px; }
+.blog-content h3 { font-size: 18px; }
+.blog-content h4,
+.blog-content h5 { font-size: 16px; }
+.blog-content p { margin-bottom: 12px; }
+.blog-content ul,
+.blog-content ol {
+  margin: 12px 0;
+  padding-right: 22px;
+}
+.blog-content ul { list-style: disc; }
+.blog-content ol { list-style: decimal; }
+.blog-content li { margin-bottom: 6px; }
+.blog-content a {
+  color: #5559ce;
+  text-decoration: underline;
+  text-underline-offset: 3px;
+}
+.blog-content blockquote {
+  margin: 16px 0;
+  padding: 12px 16px;
+  border-right: 3px solid #f17732;
+  background: #fafafa;
+  border-radius: 8px;
+  color: #3b3b3b;
+}
+.blog-content figure { margin: 16px 0; }
+.blog-content figcaption {
+  margin-top: 8px;
+  color: #9b9b9b;
+  font-size: 13px;
+  text-align: center;
+}
+.blog-content img {
+  max-width: 100%;
+  height: auto;
+  border-radius: 8px;
+}
+/* جدول روی موبایل نباید صفحه را افقی اسکرول کند. */
+.blog-content figure.table,
+.blog-content .table-wrapper {
+  overflow-x: auto;
+}
+.blog-content table {
+  width: 100%;
+  border-collapse: collapse;
+  margin: 16px 0;
+  font-size: 14px;
+}
+.blog-content :is(th, td) {
+  border: 1px solid #e5e5e5;
+  padding: 8px 12px;
+  text-align: right;
+}
+.blog-content th {
+  background: #f5f5f5;
+  font-weight: 700;
+  color: #3b3b3b;
+}