feat(sales): fresh sales implementation

app/Domains/Sales/Http/Controllers/Company/RecurringInvoiceFrequencyController.php

@@ -0,0 +1,36 @@
+<?php
+
+namespace App\Domains\Sales\Http\Controllers\Company;
+
+use App\Domains\Sales\Models\RecurringInvoice;
+use App\Platform\Http\Controller;
+use Illuminate\Http\Request;
+
+/**
+ * Previews the moment a schedule would fire for the first time.
+ */
+class RecurringInvoiceFrequencyController extends Controller
+{
+    /**
+     * Read a cron expression and a start date, and answer with the first
+     * firing they produce.
+     *
+     * The schedule form asks for this while it is still being filled in, so
+     * nothing here is gated or written down — the date is worked out, handed
+     * back and forgotten. A start date the parser cannot read, or an
+     * expression it cannot parse, comes back as a server error rather than a
+     * validation message.
+     */
+    public function __invoke(Request $request)
+    {
+        $nextRun = RecurringInvoice::getNextInvoiceDate(
+            $request->input('frequency'),
+            $request->input('starts_at'),
+        );
+
+        return response()->json([
+            'success' => true,
+            'next_invoice_at' => $nextRun,
+        ]);
+    }
+}