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

frontend/src/components/ProjectSelector.tsx

@@ -1,4 +1,5 @@
-import { Select, Button, Space, Tooltip } from 'antd';
+import { useEffect } from 'react';
+import { Select, Button, Space, Tooltip, Spin } from 'antd';
 import { PlusOutlined, EditOutlined, FolderOpenOutlined } from '@ant-design/icons';
 import { useProjectStore } from '../stores/useProjectStore';
 
@@ -6,11 +7,18 @@ export const ProjectSelector = () => {
   const {
     currentProject,
     projects,
+    loading,
     setCurrentProject,
     setShowCreateDialog,
     setShowEditDialog,
+    fetchProjects,
   } = useProjectStore();
 
+  // 组件挂载时获取项目列表
+  useEffect(() => {
+    fetchProjects();
+  }, [fetchProjects]);
+
   const handleProjectChange = (projectId: string) => {
     if (projectId === 'global') {
       setCurrentProject(null);
@@ -29,23 +37,25 @@ export const ProjectSelector = () => {
         <span className="text-sm font-medium text-gray-700">当前项目</span>
       </div>
       
-      <Space.Compact block>
-        <Select
-          value={currentProject?.id || 'global'}
-          onChange={handleProjectChange}
-          style={{ width: '100%' }}
-          placeholder="选择项目"
-        >
-          <Select.Option value="global">
-            <span className="text-blue-600">全局快速问答</span>
-          </Select.Option>
-          
-          {projects.map((project) => (
-            <Select.Option key={project.id} value={project.id}>
-              {project.name}
+      <Spin spinning={loading} size="small">
+        <Space.Compact block>
+          <Select
+            value={currentProject?.id || 'global'}
+            onChange={handleProjectChange}
+            style={{ width: '100%' }}
+            placeholder="选择项目"
+            loading={loading}
+          >
+            <Select.Option value="global">
+              <span className="text-blue-600">全局快速问答</span>
             </Select.Option>
-          ))}
-        </Select>
+            
+            {projects.map((project) => (
+              <Select.Option key={project.id} value={project.id}>
+                {project.name}
+              </Select.Option>
+            ))}
+          </Select>
         
         <Tooltip title="创建新项目">
           <Button
@@ -64,11 +74,12 @@ export const ProjectSelector = () => {
         )}
       </Space.Compact>
       
-      {currentProject && (
-        <div className="mt-2 text-xs text-gray-500 truncate">
-          {currentProject.background || '未设置项目背景'}
-        </div>
-      )}
+        {currentProject && (
+          <div className="mt-2 text-xs text-gray-500 truncate">
+            {currentProject.background || '未设置项目背景'}
+          </div>
+        )}
+      </Spin>
     </div>
   );
 };