M39: harden application and acceptance gates

backend/app/api/routers/data_quality.py

@@ -75,6 +75,7 @@ def list_issues(
     severity: str | None = Query(default=None),
     assigned_to_ref: str | None = Query(default=None),
     overdue: bool | None = Query(default=None),
+    demo_only: bool | None = Query(default=None),
     page: int | None = Query(default=None, ge=1),
     page_size: int = Query(default=25, ge=1, le=25),
     db: Session = Depends(get_db),
@@ -107,6 +108,10 @@ def list_issues(
             DataQualityIssue.status == "open",
             DataQualityIssue.due_at < datetime.now(UTC),
         )
+    if demo_only is True:
+        # Server-side so the guided demo scenarios are found on any page, not only the
+        # 25 rows currently loaded in the browser.
+        stmt = stmt.where(DataQualityIssue.public_ref.like("DQ-DEMO-%"))
     total = db.scalar(select(func.count()).select_from(stmt.subquery())) or 0
     page_number = page or 1
     issues = db.scalars(