feat(pl): filter plans by delivery-stop date range

Add EXISTS on pl_plan_delivery.delivery_time for list column filters.

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/tests/test_pl_plan_list_filters.py

@@ -120,3 +120,33 @@ def test_hazard_cert_ready_single():
     )
     assert len(filters) == 1
     assert "hazard_cert_ready" in _compile(filters[0])
+
+
+def test_delivery_time_range_exists_requires_db():
+    filters = build_plan_column_filters(
+        db=None,
+        tenant_no="shanxia2.0",
+        delivery_time_from=date(2026, 9, 12),
+        delivery_time_to=date(2026, 9, 14),
+    )
+    assert filters == []
+
+
+def test_delivery_time_range_exists_sql():
+    from unittest.mock import MagicMock
+
+    db = MagicMock()
+    q = MagicMock()
+    db.query.return_value = q
+    q.filter.return_value = q
+    q.exists.return_value = "DELIVERY_TIME_EXISTS"
+
+    filters = build_plan_column_filters(
+        db=db,
+        tenant_no="shanxia2.0",
+        delivery_time_from=date(2026, 9, 12),
+        delivery_time_to="2026-09-14",
+    )
+    assert filters == ["DELIVERY_TIME_EXISTS"]
+    assert db.query.called
+    assert q.exists.called