fix(workflow): ADR-021 code review fixes (8 bugs)

- fix(transmittal): guard duplicate workflow instance on submit()
- fix(workflow-guard): add organizationId to context so Level-2 RBAC works
- fix(circulation): organizationId context passed relation object not INT FK
- fix(transmittal): require Idempotency-Key header on POST submit endpoint
- fix(workflow): userId non-optional in processTransition controller
- fix(circulation): auto-close counts PENDING and IN_PROGRESS tasks
- fix(transmittal): status badge uses workflowState/DRAFT not purpose field
- fix(workflow): log cache invalidation failures instead of swallowing
- fix(workflow): implement getAvailableActions endpoint stub
- fix(i18n): add removeFile key to EN/TH locales

frontend/public/locales/en/common.json

@@ -29,6 +29,7 @@
   "workflow.timeline.uploading": "Uploading...",
   "workflow.timeline.uploadTypes": "PDF, DOCX, XLSX, DWG, ZIP · Max 50 MB",
   "workflow.timeline.uploadError": "Unable to upload",
+  "workflow.timeline.removeFile": "Remove file",
 
   "filePreview.fallbackTitle": "File",
   "filePreview.fileUnavailable": "File has been removed from storage.",

frontend/public/locales/th/common.json

@@ -29,6 +29,7 @@
   "workflow.timeline.uploading": "กำลังอัปโหลด...",
   "workflow.timeline.uploadTypes": "PDF, DOCX, XLSX, DWG, ZIP · สูงสุด 50 MB",
   "workflow.timeline.uploadError": "ไม่สามารถอัปโหลด",
+  "workflow.timeline.removeFile": "ลบไฟล์",
 
   "filePreview.fallbackTitle": "ไฟล์",
   "filePreview.fileUnavailable": "ไฟล์ถูกลบออกจาก Storage แล้ว",