fix(pos): resolve integration test failures for CFDI + accounting

- Fix sat_accounts.sql: split multi-row INSERT into individual statements
  so parent_id subqueries resolve correctly (was producing all NULLs)
- Add tenant_config table to v1.0 schema (required by CFDI invoicing)
- Seed tenant_config with RFC/regimen during tenant provisioning
- Fix cancel_sale to pass complete sale data for accounting reversal
- Fix CFDI XML builder: use `or` instead of dict.get() defaults to
  handle explicit None values from DB (clave_prod_serv, clave_unidad)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

pos/migrations/v1.0_initial.sql

@@ -375,5 +375,14 @@ CREATE TABLE IF NOT EXISTS physical_count_lines (
     difference INTEGER NOT NULL
 );
 
+-- =====================
+-- TENANT CONFIGURATION (key-value store for CFDI, Horux, etc.)
+-- =====================
+CREATE TABLE IF NOT EXISTS tenant_config (
+    key             VARCHAR(100) PRIMARY KEY,
+    value           TEXT,
+    updated_at      TIMESTAMPTZ DEFAULT NOW()
+);
+
 -- Barcode sequence
 CREATE SEQUENCE IF NOT EXISTS barcode_seq START 1;