feat(admin): rich text editor for blog content (TipTap)

Blog post bodies were plain <textarea>s labelled "Markdown". Replace with a
TipTap rich editor (bold/italic/strike, H1–H3, lists, blockquote, code, links,
undo/redo), RTL-aware, producing HTML.

- New RichTextEditor component (TipTap v2: react + starter-kit + pm + link +
  placeholder), immediatelyRender:false for Next SSR, self-contained content
  styling, external-value sync.
- Wired into the FA/EN content fields of the blog editor; labels no longer say
  "Markdown" (fa/en/ar).
- Website blog page now renders HTML when the body is HTML and falls back to
  MDXRemote for older Markdown posts (backward-compatible). Content is authored
  only by trusted SystemAdmins, so HTML is stored/rendered directly.

Admin build + website typecheck clean.

web/website/src/app/[locale]/blog/[slug]/page.tsx

@@ -126,7 +126,12 @@ export default async function BlogPostPage({
         {/* Content */}
         <div className="mx-auto max-w-3xl px-4 py-12 sm:px-6 lg:px-8">
           <div className="prose prose-sm sm:prose-base prose-gray max-w-none prose-headings:font-bold prose-headings:text-gray-900 prose-a:text-brand-700 prose-strong:text-gray-900">
-            <MDXRemote source={post.content} />
+            {/* New posts are authored as HTML (rich editor); older posts are MDX/Markdown. */}
+            {/^\s*</.test(post.content) ? (
+              <div dangerouslySetInnerHTML={{ __html: post.content }} />
+            ) : (
+              <MDXRemote source={post.content} />
+            )}
           </div>
 
           {/* Back link */}