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

backend/test-pkb-migration.http

@@ -163,3 +163,6 @@ DELETE {{baseUrl}}/api/v2/pkb/knowledge/knowledge-bases/{{testKbId}}
 
 
 
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