feat(server): add attachment schemas and GET /attachment/categories

Co-Authored-By: Claude <noreply@anthropic.com>

app/api/v1/attachment.py

@@ -0,0 +1,22 @@
+from fastapi import APIRouter, Depends
+from sqlalchemy.orm import Session
+
+from app.core.database import get_db
+from app.models.attachment import AttachmentCategory
+from app.schemas.attachment import CategoryResponse
+
+router = APIRouter(tags=["attachment"])
+
+
+@router.get("/attachment/categories", response_model=list[CategoryResponse])
+def list_categories(db: Session = Depends(get_db)):
+    """列出启用中的附件类型，按 sort_order、name 排序。"""
+    rows = (
+        db.query(AttachmentCategory)
+        .filter(AttachmentCategory.is_active == True)
+        .order_by(AttachmentCategory.sort_order, AttachmentCategory.name)
+        .all()
+    )
+    return [
+        CategoryResponse(id=r.id, name=r.name, sort_order=r.sort_order) for r in rows
+    ]