mcs150: only check Q29 passenger-cert box for passenger carriers

certifyBox is the Q29 Passenger Carrier Compliance Certification YES box
(page 3, y=530), not a general perjury checkbox. It was being checked
unconditionally, which wrongly marked freight/property carriers as passenger
carriers. Now only check it when the carrier is a passenger carrier; the
Q31 perjury declaration is made via the signature.

scripts/document_gen/templates/mcs150_pdf_filler.py

@@ -261,9 +261,17 @@ def fill_mcs150(intake: dict, order_number: str = "") -> str:
         if cargo in CARGO_TYPE_MAP:
             checkbox_on[CARGO_TYPE_MAP[cargo]] = True
 
-    # The bottom certification ("I ... certify ...") box is always checked --
-    # the client signs the perjury certification.
-    checkbox_on["certifyBox"] = True
+    # Q29 Passenger Carrier Compliance Certification "YES" box. Only motor
+    # passenger carriers certify here -- leave it unchecked for freight/property
+    # carriers. (The Q31 perjury declaration is made via the signature, not a
+    # checkbox.)
+    is_passenger = (
+        intake.get("is_passenger_carrier") == "yes"
+        or carrier_op in ("private_passengers_business", "private_passengers_non_business",
+                          "private_passengers")
+    )
+    if is_passenger:
+        checkbox_on["certifyBox"] = True
 
     # ── Radio-button groups (value /0../4, not /Yes) ─────────────────
     # These are single-select radio fields; the selected option index is the