fix(pkb): fix create KB and upload issues - remove simulated upload, fix department mapping, add upload modal

Fixed issues:
- Remove simulateUpload function from DashboardPage Step 3
- Map department to description field when creating KB
- Add upload modal in WorkspacePage knowledge assets tab
- Fix DocumentUpload import path (../../stores to ../stores)

Known issue: Dify API validation error during document upload (file uploaded but DB record failed, needs investigation)

Testing: KB creation works, upload dialog opens correctly

docs/08-项目管理/2026-01-11-数据库事故总结.md

@@ -202,3 +202,6 @@ VALUES ('user-mock-001', '13800000000', ..., 'tenant-mock-001', ...);
 
 > **声明**：本次事故发生在测试环境，未影响生产数据。但暴露的问题同样可能在生产环境发生，需要高度重视。
 
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