feat(inventory): show ID column, add quick-entry button, improve purchase UX

- Add ID column to stock table header and renderInventoryRow
- Add 'Entrada' button on each stock row to open purchase modal pre-filled
- Show inventory ID in product detail popup
- recordPurchase: close modal, clear form, reload stats and stock list on success
- Fix colspan 11 -> 12 for empty state rows

pos/templates/inventory.html

@@ -317,6 +317,7 @@
               <table class="data-table" id="stockTable">
                 <thead>
                   <tr>
+                    <th style="font-size:var(--text-caption);color:var(--color-text-muted);">ID</th>
                     <th>Barcode</th>
                     <th>No. Parte</th>
                     <th>Nombre</th>