fix: quality audit — memory leaks, dead prose classes, stale state scope

- safe-markdown: add `cancelled` flag to async useEffect; no more
  setState after unmount when component is destroyed mid-import
- rich-editor: same cleanup for preview tab effect; also remove dead
  `prose prose-sm max-w-none` classes (Tailwind Typography not installed)
  and replace with explicit arbitrary-selector markdown styling that
  actually renders using existing design tokens
- profile-certificate-slot: drop dead `ORDER_LABEL`, `order` variable,
  and `physicalOrder` from `MineCertificateResponse`; physical orders
  are disabled — these were leftover references causing lint noise
- learning-panel: change `issuingCert: boolean` → `issuingCertFor:
  number | null` so only the targeted user's button shows a spinner;
  a boolean shared across all users caused the wrong row to animate
  when the admin switched selected users mid-request

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/components/safe-markdown.tsx

@@ -16,14 +16,19 @@ export function SafeMarkdown({
 
   useEffect(() => {
     if (!text) { setHtml(""); return; }
+    let cancelled = false;
     void (async () => {
       const { marked } = await import("marked");
       const DOMPurify = (await import("dompurify")).default;
       const raw = await marked(text);
-      setHtml(DOMPurify.sanitize(raw));
+      if (!cancelled) setHtml(DOMPurify.sanitize(raw));
     })();
+    return () => { cancelled = true; };
   }, [text]);
 
+  const mdClasses =
+    "[&_strong]:font-bold [&_em]:italic [&_code]:rounded [&_code]:bg-muted [&_code]:px-1 [&_code]:text-[0.85em] [&_h2]:text-base [&_h2]:font-bold [&_h2]:mt-3 [&_h3]:text-sm [&_h3]:font-bold [&_h3]:mt-2 [&_ul]:list-disc [&_ul]:pr-5 [&_ol]:list-decimal [&_ol]:pr-5 [&_li]:mt-0.5 [&_p]:leading-relaxed [&_p+p]:mt-2 [&_a]:underline [&_a]:text-primary";
+
   if (!html) {
     return (
       <div
@@ -45,7 +50,8 @@ export function SafeMarkdown({
     <div
       dir="auto"
       className={cn(
-        "prose prose-sm max-w-none break-words [unicode-bidi:plaintext]",
+        "break-words text-sm [unicode-bidi:plaintext]",
+        mdClasses,
         lines === 2 && "line-clamp-2",
         lines === 3 && "line-clamp-3",
         className,