Fix inline emphasis tags in markdown output

- Without strong, **bold** rendered as plain text since marked
  emits <strong> and DOMPurify stripped the unknown tag
- Add strong, b, i, del, s to DOMPurify allow-list
- Cover the other inline emphasis tags authors may write as raw
  HTML or that GFM strikethrough emits (<del>)

src/lib/markdown.ts

@@ -31,14 +31,17 @@ dompurify.setConfig({
   ],
   ALLOWED_TAGS: [
     "a",
+    "b",
     "blockquote",
     "br",
     "code",
     "dd",
+    "del",
     "div",
     "dl",
     "dt",
     "em",
+    "i",
     "h1",
     "h2",
     "h3",
@@ -53,6 +56,8 @@ dompurify.setConfig({
     "p",
     "pre",
     "radicle-external-link",
+    "s",
+    "strong",
     "table",
     "tbody",
     "td",