feat(crm): per-customer Skonto opt-out

Adds customer_accounts.skonto_disabled (migration 112) so a customer
that negotiated "no early-payment discount" can be flagged once instead
of ticking the per-invoice toggle on every invoice. resolveSkontoPercent
ForInvoice and the PDF render context both honour it, extending the
resolution chain to customer → invoice → snapshot → quote → global.
Checkbox added to the customer detail Billing card (en + de).

backend/migrations/core/112_add_customer_skonto_disabled.js

@@ -0,0 +1,34 @@
+/**
+ * Migration: per-customer Skonto opt-out.
+ *
+ * Background: invoices already carry a per-invoice `skonto_disabled`
+ * flag (migration 126). For B2B customers who negotiated "no early-
+ * payment discount" as a standing contract term, the admin had to tick
+ * that toggle on every single invoice. This adds a customer-level flag
+ * so the opt-out is set once and applies to all of that customer's
+ * invoices. The resolver chain becomes:
+ *   customer.skonto_disabled → invoice.skonto_disabled →
+ *   invoice snapshot → source-quote snapshot → global default.
+ *
+ * Default false so existing customers keep inheriting whatever Skonto
+ * the template / global default offers — no behaviour change on upgrade
+ * (see migration-preserve-existing-state guidance).
+ *
+ * Idempotent: guarded by hasColumn so a re-run is a no-op.
+ */
+
+exports.up = async function(knex) {
+  if (!(await knex.schema.hasTable('customer_accounts'))) return;
+  if (await knex.schema.hasColumn('customer_accounts', 'skonto_disabled')) return;
+  await knex.schema.alterTable('customer_accounts', (table) => {
+    table.boolean('skonto_disabled').notNullable().defaultTo(false);
+  });
+};
+
+exports.down = async function(knex) {
+  if (!(await knex.schema.hasTable('customer_accounts'))) return;
+  if (!(await knex.schema.hasColumn('customer_accounts', 'skonto_disabled'))) return;
+  await knex.schema.alterTable('customer_accounts', (table) => {
+    table.dropColumn('skonto_disabled');
+  });
+};

backend/src/routes/adminCustomers.js

@@ -67,6 +67,10 @@ function transformCustomer(c) {
     // per-entry override on every logged block.
     featureHoursLogging: c.feature_hours_logging === true || c.feature_hours_logging === 1,
     hourlyRateMinor: c.hourly_rate_minor != null ? Number(c.hourly_rate_minor) : null,
+    // Per-customer Skonto opt-out (migration 112). When true, none of
+    // this customer's invoices qualify for an early-payment discount,
+    // regardless of template / global defaults.
+    skontoDisabled: c.skonto_disabled === true || c.skonto_disabled === 1,
     lastLogin: c.last_login,
     createdAt: c.created_at,
     updatedAt: c.updated_at,
@@ -394,6 +398,8 @@ router.put('/:id', [
   body('billing_cadence').optional().isIn(['per_event', 'monthly', 'quarterly']),
   body('billing_cycle_day').optional().isInt({ min: -15, max: 28 })
     .withMessage('billing_cycle_day must be -15..-1 (days before month end) or 1..28 (day of month)'),
+  // Per-customer Skonto opt-out (migration 112).
+  body('skonto_disabled').optional().isBoolean(),
 ], handleAsync(async (req, res) => {
   validateRequest(req);
   const customer = await customerAccountsService.updateCustomer(

backend/src/services/customerAccountsService.js

@@ -555,6 +555,9 @@ async function updateCustomer(id, updates, updatedByAdminId) {
     // Hour-logging default rate (migration 129). Minor units; null
     // means admin must enter a per-entry override on every entry.
     'hourly_rate_minor',
+    // Per-customer Skonto opt-out (migration 112). Boolean, coerced
+    // via formatBoolean below for SQLite compatibility.
+    'skonto_disabled',
   ];
   for (const f of fields) {
     if (updates[f] !== undefined) {
@@ -567,6 +570,7 @@ async function updateCustomer(id, updates, updatedByAdminId) {
       } else if (
         f === 'feature_calendar' || f === 'feature_quotes'
         || f === 'feature_bills' || f === 'feature_hours_logging'
+        || f === 'skonto_disabled'
       ) {
         allowed[f] = formatBoolean(updates[f]);
       } else if (f === 'hourly_rate_minor') {

backend/src/services/invoiceService.js

@@ -1690,8 +1690,10 @@ async function buildInvoiceRenderContext(invoice, lineItems) {
   // but still printed the discount row on the PDF. Zero out both
   // fields here so pdfService.drawPaymentBlock's
   // `paymentTerm?.skontoPercent && paymentTerm?.skontoWithinDays`
-  // guard suppresses the row.
-  if (invoice.skonto_disabled) {
+  // guard suppresses the row. The per-customer opt-out (migration 112)
+  // is honoured here too — a customer flagged skonto_disabled never
+  // prints the discount row, mirroring resolveSkontoPercentForInvoice.
+  if (invoice.skonto_disabled || customer?.skonto_disabled) {
     paymentTerm.skontoPercent = null;
     paymentTerm.skontoWithinDays = null;
   }
@@ -2667,6 +2669,17 @@ async function resolveSkontoPercentForInvoice(invoice) {
   // installments that shouldn't qualify for the discount even when
   // the global default offers it.
   if (invoice.skonto_disabled) return null;
+  // Per-customer opt-out (migration 112) — a customer that negotiated
+  // "no Skonto" as a contract term never qualifies, so the admin
+  // doesn't have to tick the per-invoice toggle on every invoice.
+  // Falls through customer → invoice → snapshot → quote → global.
+  if (invoice.customer_account_id) {
+    const cust = await db('customer_accounts')
+      .where({ id: invoice.customer_account_id })
+      .select('skonto_disabled')
+      .first();
+    if (cust && cust.skonto_disabled) return null;
+  }
   const parseSnap = (raw) => {
     if (!raw) return null;
     if (typeof raw === 'object') return raw;