Add Ladill POS v1 — register, Pay checkout, and commerce links.

Staff-facing counter register at pos.ladill.com with catalog cart, cash and
MoMo/card checkout via Ladill Pay, CRM timeline/import, invoice prefill, and
Merchant catalog import.

Co-authored-by: Cursor <cursoragent@cursor.com>

app/Models/PosSaleLine.php

@@ -0,0 +1,39 @@
+<?php
+
+namespace App\Models;
+
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\BelongsTo;
+
+class PosSaleLine extends Model
+{
+    protected $fillable = [
+        'pos_sale_id',
+        'product_id',
+        'name',
+        'unit_price_minor',
+        'quantity',
+        'line_total_minor',
+        'position',
+    ];
+
+    protected function casts(): array
+    {
+        return [
+            'unit_price_minor' => 'integer',
+            'quantity' => 'integer',
+            'line_total_minor' => 'integer',
+            'position' => 'integer',
+        ];
+    }
+
+    public function sale(): BelongsTo
+    {
+        return $this->belongsTo(PosSale::class, 'pos_sale_id');
+    }
+
+    public function product(): BelongsTo
+    {
+        return $this->belongsTo(PosProduct::class, 'product_id');
+    }
+}