refactor: preview 병렬 트리거 + 파일 이동 제거 + domain 색상 바

- queue_consumer: extract 완료 시 classify + preview 동시 등록
- classify_worker: _move_to_knowledge() 제거, 파일 원본 위치 유지
- DocumentCard: 좌측 domain별 색상 바 (4px) 추가

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

app/workers/queue_consumer.py

@@ -34,27 +34,28 @@ async def reset_stale_items():
 
 async def enqueue_next_stage(document_id: int, current_stage: str):
     """현재 stage 완료 후 다음 stage를 pending으로 등록"""
-    next_stages = {"extract": "classify", "classify": "embed", "embed": "preview"}
-    next_stage = next_stages.get(current_stage)
-    if not next_stage:
+    next_stages = {"extract": ["classify", "preview"], "classify": ["embed"]}
+    stages = next_stages.get(current_stage, [])
+    if not stages:
         return
 
     async with async_session() as session:
-        existing = await session.execute(
-            select(ProcessingQueue).where(
-                ProcessingQueue.document_id == document_id,
-                ProcessingQueue.stage == next_stage,
-                ProcessingQueue.status.in_(["pending", "processing"]),
+        for next_stage in stages:
+            existing = await session.execute(
+                select(ProcessingQueue).where(
+                    ProcessingQueue.document_id == document_id,
+                    ProcessingQueue.stage == next_stage,
+                    ProcessingQueue.status.in_(["pending", "processing"]),
+                )
             )
-        )
-        if existing.scalar_one_or_none():
-            return
+            if existing.scalar_one_or_none():
+                continue
 
-        session.add(ProcessingQueue(
-            document_id=document_id,
-            stage=next_stage,
-            status="pending",
-        ))
+            session.add(ProcessingQueue(
+                document_id=document_id,
+                stage=next_stage,
+                status="pending",
+            ))
         await session.commit()