feat(pos/facturapi): finalize Horux-to-Facturapi migration

- Normalize Facturapi key/org_id resolution (supports both cfdi_ prefixed
  tenant_config keys and short names used by invoicing_bp).
- Add CSD upload end-to-end (backend + frontend).
- Add helper scripts: setup_facturapi_orgs.py and check_facturapi_tenants.py.
- Add 20 unit tests with mocks (pos/tests/test_facturapi_service.py).
- Add CI workflow for lint + console tests on Python 3.11/3.13.
- Add pyproject.toml and requirements-dev.txt with ruff/pytest config.
- Update FASES_IMPLEMENTADAS.md with FASE 8 documentation.

Tests: 81 passing (61 console + 20 Facturapi).

pos/services/cfdi_facturapi_builder.py

@@ -9,8 +9,8 @@ generates those payloads for:
   - Factura global mensual
 """
 
-from decimal import Decimal, ROUND_HALF_UP
 from datetime import datetime
+from decimal import ROUND_HALF_UP, Decimal
 
 # SAT defaults
 RFC_PUBLICO_GENERAL = "XAXX010101000"
@@ -148,9 +148,7 @@ def build_egreso_payload(sale, tenant_config, customer, original_uuid):
     """Build Facturapi payload for a credit note (Comprobante tipo Egreso)."""
     payload = build_ingreso_payload(sale, tenant_config, customer)
     payload["type"] = "E"
-    payload["related_documents"] = [
-        {"relationship": "01", "documents": [original_uuid]}
-    ]
+    payload["related_documents"] = [{"relationship": "01", "documents": [original_uuid]}]
     payload["payment_method"] = "PUE"
     return payload
 
@@ -162,15 +160,12 @@ def build_pago_payload(payment, tenant_config, customer, original_uuid):
 
     amount = _to_dec(payment.get("amount", 0))
     base = (amount / Decimal("1.16")).quantize(TWO, ROUND_HALF_UP)
-    iva = (amount - base).quantize(TWO, ROUND_HALF_UP)
 
     payment_date = payment.get("date") or datetime.now().strftime("%Y-%m-%dT%H:%M:%S")
     if "T" not in str(payment_date):
         payment_date = f"{payment_date}T12:00:00"
 
-    forma_pago = FORMA_PAGO_MAP.get(
-        (payment.get("payment_method") or "").lower().strip(), "01"
-    )
+    forma_pago = FORMA_PAGO_MAP.get((payment.get("payment_method") or "").lower().strip(), "01")
 
     payload = {
         "type": "P",