feat: Day 8-9 - Project Management API completed

Backend:
- Create project routes (GET, POST, PUT, DELETE)
- Implement projectController with CRUD operations
- Create projectService for database operations
- Add validation middleware for request validation
- Update Prisma schema (add background, researchType, deletedAt fields)
- Implement soft delete for projects

Frontend:
- Create projectApi service module
- Update useProjectStore with fetchProjects and loading state
- Connect ProjectSelector to real API with loading indicator
- Connect CreateProjectDialog to real API with error handling
- Connect EditProjectDialog to real API with loading state
- Add comprehensive error handling and user feedback

Build: Both frontend and backend build successfully

backend/src/services/projectService.ts

@@ -0,0 +1,102 @@
+import { prisma } from '../config/database.js';
+
+export interface CreateProjectDTO {
+  name: string;
+  background: string;
+  researchType: 'observational' | 'interventional';
+  userId: string;
+}
+
+export interface UpdateProjectDTO {
+  name?: string;
+  background?: string;
+  researchType?: 'observational' | 'interventional';
+}
+
+class ProjectService {
+  // 获取用户的所有项目
+  async getProjectsByUserId(userId: string) {
+    return prisma.project.findMany({
+      where: {
+        userId,
+        deletedAt: null,
+      },
+      orderBy: {
+        createdAt: 'desc',
+      },
+    });
+  }
+
+  // 根据ID获取项目
+  async getProjectById(projectId: string, userId: string) {
+    return prisma.project.findFirst({
+      where: {
+        id: projectId,
+        userId,
+        deletedAt: null,
+      },
+    });
+  }
+
+  // 创建项目
+  async createProject(data: CreateProjectDTO) {
+    return prisma.project.create({
+      data: {
+        name: data.name,
+        background: data.background,
+        researchType: data.researchType,
+        userId: data.userId,
+      },
+    });
+  }
+
+  // 更新项目
+  async updateProject(projectId: string, userId: string, data: UpdateProjectDTO) {
+    // 先检查项目是否存在且属于该用户
+    const project = await this.getProjectById(projectId, userId);
+    if (!project) {
+      return null;
+    }
+
+    return prisma.project.update({
+      where: {
+        id: projectId,
+      },
+      data: {
+        ...data,
+        updatedAt: new Date(),
+      },
+    });
+  }
+
+  // 软删除项目
+  async deleteProject(projectId: string, userId: string) {
+    // 先检查项目是否存在且属于该用户
+    const project = await this.getProjectById(projectId, userId);
+    if (!project) {
+      return null;
+    }
+
+    return prisma.project.update({
+      where: {
+        id: projectId,
+      },
+      data: {
+        deletedAt: new Date(),
+      },
+    });
+  }
+
+  // 统计用户的项目数量
+  async countUserProjects(userId: string) {
+    return prisma.project.count({
+      where: {
+        userId,
+        deletedAt: null,
+      },
+    });
+  }
+}
+
+export const projectService = new ProjectService();
+