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).

requirements-dev.txt

@@ -0,0 +1,16 @@
+# Development dependencies for Nexus Autoparts
+# Install: pip install -r requirements-dev.txt
+
+# Testing
+pytest>=8.0
+pytest-asyncio>=0.23
+pytest-cov>=5.0
+
+# Linting and formatting
+ruff>=0.6.0
+
+# Type checking (optional, enable later)
+# mypy>=1.10
+
+# E2E testing
+# playwright>=1.40  # install via npm: npx playwright install