feat(pos): migrate CFDI timbrado from Horux to Facturapi

- Add Facturapi REST service (invoices, customers, orgs, cancel, downloads)
- Add JSON payload builder for ingreso/egreso/pago/global invoices
- Replace XML queue with Facturapi JSON queue (payload_unsigned, external_id)
- Update invoicing blueprint with Facturapi config and download endpoints
- Update global invoice service to use Facturapi payloads
- Add migration v4.3_facturapi.sql and tenant rollout script
- Update invoicing UI: payload preview, PDF/XML downloads, PAC status panel
- Add FACTURAPI_USER_KEY to .env.example

pos/migrations/v4.3_facturapi.sql

@@ -0,0 +1,34 @@
+-- v4.3_facturapi.sql
+-- Migrate CFDI timbrado from Horux360 XML pipeline to Facturapi JSON API.
+--
+-- Changes:
+--   - Rename cfdi_queue.xml_unsigned -> payload_unsigned (stores Facturapi JSON payload)
+--   - Keep xml_signed for the signed XML returned by Facturapi
+--   - Add external_id column to store Facturapi invoice id
+--   - Add facturapi config keys to tenant_config
+
+-- ═════════════════════════════════════════════════════════════════════════════
+-- 1. CFDI_QUEUE: adapt schema for Facturapi payloads
+-- ═════════════════════════════════════════════════════════════════════════════
+ALTER TABLE cfdi_queue RENAME COLUMN xml_unsigned TO payload_unsigned;
+
+COMMENT ON COLUMN cfdi_queue.payload_unsigned IS 'Facturapi JSON payload (previously unsigned XML for Horux)';
+COMMENT ON COLUMN cfdi_queue.xml_signed IS 'Signed+stamped XML returned by Facturapi';
+
+ALTER TABLE cfdi_queue ADD COLUMN IF NOT EXISTS external_id VARCHAR(64);
+COMMENT ON COLUMN cfdi_queue.external_id IS 'Facturapi invoice id';
+
+CREATE INDEX IF NOT EXISTS idx_cfdi_queue_external_id ON cfdi_queue(external_id);
+
+-- ═════════════════════════════════════════════════════════════════════════════
+-- 2. TENANT_CONFIG: Facturapi configuration keys
+-- ═════════════════════════════════════════════════════════════════════════════
+INSERT INTO tenant_config (key, value)
+VALUES
+    ('cfdi_facturapi_key', ''),
+    ('cfdi_facturapi_org_id', ''),
+    ('cfdi_facturapi_customer_sync', 'true')
+ON CONFLICT (key) DO NOTHING;
+
+-- Backward-compat: migrate old Horux keys to comments so they are not used anymore
+COMMENT ON TABLE tenant_config IS 'tenant_config; old keys cfdi_horux_api_url and cfdi_horux_api_key are deprecated';