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/temp_check.sql

@@ -1,2 +1,5 @@
 SELECT schema_name FROM information_schema.schemata WHERE schema_name NOT IN ('pg_catalog', 'information_schema', 'pg_toast') ORDER BY schema_name;
 
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