feat: 问题数据迁移到数据库；学员详情页URL导航改造；侧边栏统一

- 问题从文件系统迁移到数据库 problems 表
- 移除 PROBLEMS_DIR 配置和文件读取逻辑
- student.html 完整重写：编辑/添加/删除问题，生成方案进度显示
- 学员详情页支持独立URL访问 (/student/<id>)
- 统一侧边栏到 base.html
- 更新文档：DEPLOYMENT_SOP, MODELS, STRUCTURE, FRONTEND_ARCH
- 部署到生产环境 v1.2.0

app/services/plan_generator.py

@@ -7,15 +7,14 @@ from app.config import load_api_config
 
 
 def generate_practice_plan(
-    student_name, problems, problems_dir, practice_time="30-60分钟"
+    student_name, problems, practice_time="30-60分钟"
 ):
     """
     根据学员问题和练习时间生成针对性练习方案
 
     Args:
         student_name: 学员姓名
-        problems: 问题列表 [{problem_id, problem_name, severity}]
-        problems_dir: 问题文件所在目录
+        problems: 问题列表 [{problem_id, problem_name, severity, level, content}]
         practice_time: 练习时间描述
 
     Returns:
@@ -34,39 +33,20 @@ def generate_practice_plan(
     }
     time_config = time_mapping.get(practice_time, time_mapping["30分钟"])
 
-    # 读取问题文件内容
+    # 从数据库问题内容构建
     problem_contents = []
     for p in problems:
-        problem_file = os.path.join(problems_dir, f"{p['problem_id']}.md")
-        if os.path.exists(problem_file):
-            with open(problem_file, "r", encoding="utf-8") as f:
-                content = f.read()
-                # 提取关键部分
-                problem_contents.append(
-                    {
-                        "name": p["problem_name"],
-                        "severity": p["severity"],
-                        "content": _extract_key_sections(content),
-                        "time_allocation": _calculate_time_allocation(
-                            p["severity"], time_config
-                        ),
-                    }
-                )
-        else:
-            # 问题文件不存在时，使用默认内容
-            problem_contents.append(
-                {
-                    "name": p["problem_name"],
-                    "severity": p["severity"],
-                    "content": {
-                        "problem": f"针对{p['problem_name']}的练习",
-                        "suggestion": "建议每天进行针对性练习",
-                    },
-                    "time_allocation": _calculate_time_allocation(
-                        p["severity"], time_config
-                    ),
-                }
-            )
+        content = p.get("content", "") or ""
+        problem_contents.append(
+            {
+                "name": p["problem_name"],
+                "severity": p["severity"],
+                "content": _extract_key_sections(content) if content else {"problem": f"针对{p['problem_name']}的练习"},
+                "time_allocation": _calculate_time_allocation(
+                    p["severity"], time_config
+                ),
+            }
+        )
 
     # 生成每日练习计划
     daily_plan = _generate_daily_schedule(time_config, problem_contents)