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/package.json

@@ -9,23 +9,23 @@
     "lint": "next lint"
   },
   "dependencies": {
+    "axios": "^1.7.9",
+    "lucide-react": "^0.469.0",
     "next": "^15.3.1",
     "react": "^19.1.0",
     "react-dom": "^19.1.0",
-    "axios": "^1.7.9",
-    "zustand": "^5.0.3",
-    "react-markdown": "^9.0.3",
-    "lucide-react": "^0.469.0"
+    "react-markdown": "^9.1.0",
+    "zustand": "^5.0.3"
   },
   "devDependencies": {
-    "typescript": "^5.7.3",
+    "@eslint/eslintrc": "^3",
+    "@tailwindcss/postcss": "^4.1.0",
     "@types/node": "^22.10.0",
     "@types/react": "^19.1.0",
     "@types/react-dom": "^19.1.0",
-    "@tailwindcss/postcss": "^4.1.0",
-    "tailwindcss": "^4.1.0",
     "eslint": "^9.17.0",
     "eslint-config-next": "^15.3.1",
-    "@eslint/eslintrc": "^3"
+    "tailwindcss": "^4.1.0",
+    "typescript": "^5.7.3"
   }
 }