Add English level settings, improve content structuring and rendering

- Add english_level column to users table (CEFR with TOEIC mapping)
- Add UserController (GET/PATCH /api/users/me) and Settings page
- Enhance structuring prompts: sequential TOC, no summary sections,
  no content overlap, English expression extraction by CEFR level
- Remove sub-TOC analysis (caused content repetition), use simple
  per-section generation with truncation detection and continuation
- Fix CLOB truncation: explicit Clob-to-String conversion in repository
- Replace regex-based markdown rendering with react-markdown
- Add wallet renewal procedure to troubleshooting docs

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

sundol-frontend/src/app/knowledge/[id]/page.tsx

@@ -5,6 +5,7 @@ import { useParams, useRouter } from "next/navigation";
 import AuthGuard from "@/components/auth-guard";
 import NavBar from "@/components/nav-bar";
 import { useApi } from "@/lib/use-api";
+import ReactMarkdown from "react-markdown";
 
 interface Category {
   ID: string;
@@ -306,19 +307,25 @@ export default function KnowledgeDetailPage() {
               {showStructured ? "▼ 정리된 내용 숨기기" : "▶ 정리된 내용 보기"}
             </button>
             {showStructured && (
-              <div className="bg-[var(--color-bg-card)] rounded-xl p-6 border border-[var(--color-border)] prose prose-invert max-w-none">
-                <div
-                  className="text-sm leading-relaxed whitespace-pre-wrap"
-                  dangerouslySetInnerHTML={{
-                    __html: item.STRUCTURED_CONTENT
-                      .replace(/^### (.+)$/gm, '<h3 class="text-base font-bold mt-4 mb-2 text-[var(--color-text)]">$1</h3>')
-                      .replace(/^## (.+)$/gm, '<h2 class="text-lg font-bold mt-5 mb-2 text-[var(--color-text)]">$1</h2>')
-                      .replace(/^# (.+)$/gm, '<h1 class="text-xl font-bold mt-6 mb-3 text-[var(--color-text)]">$1</h1>')
-                      .replace(/\*\*(.+?)\*\*/g, '<strong>$1</strong>')
-                      .replace(/^- (.+)$/gm, '<li class="ml-4 list-disc">$1</li>')
-                      .replace(/^(\d+)\. (.+)$/gm, '<li class="ml-4 list-decimal">$2</li>')
-                  }}
-                />
+              <div className="bg-[var(--color-bg-card)] rounded-xl p-6 border border-[var(--color-border)] max-w-none">
+                <div className="structured-content text-sm leading-relaxed">
+                  <ReactMarkdown
+                    components={{
+                      h1: ({children}) => <h1 className="text-xl font-bold mt-6 mb-3">{children}</h1>,
+                      h2: ({children}) => <h2 className="text-lg font-bold mt-5 mb-2">{children}</h2>,
+                      h3: ({children}) => <h3 className="text-base font-bold mt-4 mb-2">{children}</h3>,
+                      p: ({children}) => <p className="mb-3">{children}</p>,
+                      ul: ({children}) => <ul className="list-disc ml-5 mb-3 space-y-1">{children}</ul>,
+                      ol: ({children}) => <ol className="list-decimal ml-5 mb-3 space-y-1">{children}</ol>,
+                      li: ({children}) => <li className="leading-relaxed">{children}</li>,
+                      strong: ({children}) => <strong className="font-bold">{children}</strong>,
+                      blockquote: ({children}) => <blockquote className="border-l-2 border-[var(--color-primary)] pl-4 my-3 italic text-[var(--color-text-muted)]">{children}</blockquote>,
+                      code: ({children}) => <code className="bg-[var(--color-bg-hover)] px-1.5 py-0.5 rounded text-xs">{children}</code>,
+                    }}
+                  >
+                    {item.STRUCTURED_CONTENT}
+                  </ReactMarkdown>
+                </div>
               </div>
             )}
           </div>