feat: add a read-only Jadlog price probe

app/jadlog.py prices one package through Jadlog's Simulador de Frete as the
API manual v2.3 describes it; app.jadlog_probe prices test weights to six
regions on the client's account to confirm token, account and contract.
Tested against a fake transport. The roadmap records the Jadlog data and the
Mercado Pago account setup.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.env.example

@@ -37,6 +37,11 @@ TINY_ADAPTER=fake
 # TINY_PRODUCT_UV_FOLHA=...
 # TINY_PRODUCT_UV_AVULSA=...
 # TINY_ADAPTER=tiny      # only once connected and tested: creates real orders
+# Jadlog price quotes go in jadlog.env, not here (see app/jadlog_probe.py):
+# JADLOG_TOKEN=...
+# JADLOG_CNPJ=...          # the "Usuário" Jadlog issued, the CNPJ that contracts freight
+# JADLOG_CONTA=...         # conta corrente
+# JADLOG_CONTRATO=         # only if Jadlog issued a contract number
 WHATSAPP_ADAPTER=fake
 STORAGE_ADAPTER=s3-local
 MOCK_FREIGHT_CENTS=1500