Normalize RdSAP percent_draughtproofed on the 21.0.0 path

PRD #1385 phase 2. 21.0.0 was the last mapper still dropping the lodged
percent_draughtproofed (top-level int) — every other path (17.0/…/21.0.1) reads
it. Dropping it understated the SAP §2 draughtproofing/infiltration credit for
21.0.0 certs.

Verification: new test 1 passed (harvested 21.0.0 sample lodges 100); corpus
6002 passed; SAP-accuracy regressions pass; pyright unchanged (39 -> 39).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

datatypes/epc/domain/mapper.py

@@ -2142,6 +2142,10 @@ class EpcPropertyDataMapper:
             open_chimneys_count=schema.open_chimneys_count or 0,
             insulated_door_count=schema.insulated_door_count,
             draughtproofed_door_count=schema.draughtproofed_door_count,
+            # 21.0.0 lodges percent_draughtproofed but the mapper dropped it,
+            # unlike every other path (17.0/…/21.0.1). Understated the §2
+            # draughtproofing/infiltration credit.
+            percent_draughtproofed=schema.percent_draughtproofed,
             led_fixed_lighting_bulbs_count=schema.led_fixed_lighting_bulbs_count or 0,
             cfl_fixed_lighting_bulbs_count=schema.cfl_fixed_lighting_bulbs_count or 0,
             incandescent_fixed_lighting_bulbs_count=schema.incandescent_fixed_lighting_bulbs_count,

tests/datatypes/epc/domain/test_mapper_percent_draughtproofed_21_0_0.py

@@ -0,0 +1,34 @@
+"""Regression: the RdSAP-Schema-21.0.0 mapper must carry the lodged
+percent_draughtproofed, like every other API path (17.0/…/21.0.1).
+
+PRD #1385 (mapper normalization). 21.0.0 was the last path still dropping
+`percent_draughtproofed` (top-level int, lodged by the schema), understating the
+§2 draughtproofing/infiltration credit.
+"""
+
+from __future__ import annotations
+
+import json
+from pathlib import Path
+from typing import Any
+
+from datatypes.epc.domain.mapper import EpcPropertyDataMapper
+
+# The harvested 21.0.0 sample lodges percent_draughtproofed=100.
+_FIXTURE = Path("backend/epc_api/json_samples/RdSAP-Schema-21.0.0/epc.json")
+
+
+def _load() -> dict[str, Any]:
+    data: dict[str, Any] = json.loads(_FIXTURE.read_text())
+    assert data["schema_type"] == "RdSAP-Schema-21.0.0"
+    return data
+
+
+def test_21_0_0_carries_percent_draughtproofed() -> None:
+    data = _load()
+    assert data["percent_draughtproofed"] == 100
+
+    epc = EpcPropertyDataMapper.from_api_response(data)
+
+    # Was dropped to None on the 21.0.0 path; now carried through.
+    assert epc.percent_draughtproofed == 100