S0380.237: map "Secondary glazing - Low emissivity" → SAP 10.2 code 12

Completes the secondary-glazing family. S0380.235 mapped the unknown-data
(7) and normal-emissivity (11) secondary variants; the RdSAP-21.0.1
`glazed_type` enum also defines code 12 "secondary glazing, low
emissivity", whose Elmhurst §11 label "Secondary glazing - Low
emissivity" was unmapped and would strict-raise. Cascade code 12 carries
the same daylight/solar bucket as 7/11 (g_L=0.80, g⊥=0.76); the lodged
manufacturer U/g drive §3/§6. With this the double family (codes 1/2/3/
7/13 via their Elmhurst phrasings) and the secondary family (4/11/12) are
fully covered. Coverage test extended.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/documents_parser/tests/test_summary_pdf_mapper_chain.py

@@ -1489,6 +1489,7 @@ def test_elmhurst_glazing_label_full_coverage_per_sap10_table_6b() -> None:
         "Double post or during 2022": 5,
         "Secondary glazing": 7,
         "Secondary glazing - Normal emissivity": 11,
+        "Secondary glazing - Low emissivity": 12,
         "Triple pre 2002": 10,
         "Triple between 2002 and 2021": 9,
         "Triple post or during 2022": 6,

datatypes/epc/domain/mapper.py

@@ -5083,6 +5083,12 @@ _ELMHURST_GLAZING_LABEL_TO_SAP10: Dict[str, int] = {
     # fixture (Summary_001431 §11 Window 9).
     "Secondary glazing": 7,
     "Secondary glazing - Normal emissivity": 11,
+    # RdSAP-21 glazed_type 12 "secondary glazing, low emissivity" — the
+    # low-E sibling of code 11. Cascade code 12 carries g_L=0.80 / g⊥=0.76
+    # (identical daylight/solar bucket to 7 and 11; the lodged U/g drive
+    # §3/§6). Mapped symmetrically with the "Normal emissivity" variant so
+    # the whole secondary-glazing family is covered.
+    "Secondary glazing - Low emissivity": 12,
     # RdSAP-21 row "triple glazing, installed pre-2002" (cascade code 10,
     # g_L=0.70, g⊥=0.68 — same triple-glazed daylight/solar bucket as the
     # other triple variants {6, 8, 9, 14}). The lodged manufacturer