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/admin/package.json

@@ -15,10 +15,15 @@
     "@radix-ui/react-label": "^2.1.0",
     "@radix-ui/react-slot": "^1.1.0",
     "@tanstack/react-query": "^5.59.20",
+    "@tiptap/extension-link": "^2.27.2",
+    "@tiptap/extension-placeholder": "^2.27.2",
+    "@tiptap/pm": "^2.27.2",
+    "@tiptap/react": "^2.27.2",
+    "@tiptap/starter-kit": "^2.27.2",
     "axios": "^1.7.7",
-    "date-fns-jalali": "^4.1.0-0",
     "class-variance-authority": "^0.7.0",
     "clsx": "^2.1.1",
+    "date-fns-jalali": "^4.1.0-0",
     "lucide-react": "^0.454.0",
     "next": "14.2.18",
     "next-intl": "^3.23.5",