fix(mcs150): point intake email to per-slug wizard (not sales page) + add Trailers field

The MCS-150 intake-completion email linked customers to /order/dot-compliance,
which is the sales/checkout page -- it ignores ?order= and asks the customer to
re-pick services and pay again, so they 'cannot enter any data' (Paul Wilson's
report). Link to the per-service intake wizard /order/<slug>?order=... instead,
which loads the paid order, pre-fills from the FMCSA census, and drops payment.

Also add a Trailers field to the DOT intake fleet section and wire it through to
the MCS-150 PDF Q26 trailer row, so carriers can update trucks AND trailers.

scripts/document_gen/templates/mcs150_pdf_filler.py

@@ -319,6 +319,11 @@ def fill_mcs150(intake: dict, order_number: str = "") -> str:
             intake.get("primary_vehicle_type", "straight"), "straight")
         if power_units not in (None, ""):
             field_updates[f"{prefix}Own"] = str(power_units)
+        # Simple intake also collects a flat trailer count (no owned/leased
+        # breakdown). Default trailers to the Owned column of the trailer row.
+        trailers = intake.get("trailers", "")
+        if trailers not in (None, "", 0, "0"):
+            field_updates["trailerOwn"] = str(trailers)
 
     # Non-CMV count, if provided.
     if intake.get("non_cmv_vehicles") not in (None, ""):