feat(ai): unify AI architecture, implement RAG and legacy migration

frontend/public/locales/en/common.json

@@ -37,5 +37,38 @@
   "filePreview.unsupported": "Preview is not available for this file type.",
   "filePreview.loadError": "Unable to load file. Please try again.",
   "filePreview.download": "Download",
-  "filePreview.close": "Close"
+  "filePreview.close": "Close",
+
+  "ai.status.offlineTitle": "AI unavailable",
+  "ai.status.offlineDescription": "AI staging is temporarily unavailable. Manual document operations remain available.",
+  "ai.status.onlineTitle": "AI staging available",
+  "ai.status.onlineDescription": "Legacy migration review queue is connected.",
+  "ai.staging.title": "AI Staging Queue",
+  "ai.staging.subtitle": "Review AI-extracted legacy metadata before committing it to DMS records.",
+  "ai.staging.refresh": "Refresh",
+  "ai.staging.file": "File",
+  "ai.staging.batch": "Batch",
+  "ai.staging.confidence": "Confidence",
+  "ai.staging.status": "Status",
+  "ai.staging.review": "Review",
+  "ai.staging.empty": "—",
+  "ai.staging.loading": "Loading staging records...",
+  "ai.staging.emptyQueue": "No staging records found.",
+  "ai.staging.reviewTitle": "Review AI Metadata",
+  "ai.staging.documentNumber": "Document number",
+  "ai.staging.category": "Category",
+  "ai.staging.selectCategory": "Select category",
+  "ai.staging.subject": "Subject",
+  "ai.staging.project": "Project",
+  "ai.staging.selectProject": "Select project",
+  "ai.staging.sender": "Sender",
+  "ai.staging.selectSender": "Select sender",
+  "ai.staging.receiver": "Receiver",
+  "ai.staging.selectReceiver": "Select receiver",
+  "ai.staging.issuedDate": "Issued date",
+  "ai.staging.receivedDate": "Received date",
+  "ai.staging.body": "Body",
+  "ai.staging.approve": "Approve",
+  "ai.staging.approveSuccess": "Staging record approved.",
+  "ai.staging.approveError": "Unable to approve staging record."
 }