Fix bin check zeroing bulk item quantities

Bin check was using count_last_audit (0 for bulk items) as the audit
value for all items. Now looks up product kind and uses
last_audit_weight for bulk items, only updates count_last_audit for
discrete items.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/routes/inventory.ts

@@ -455,22 +455,32 @@ inventoryRouter.post("/bins/:id/check", (req, res) => {
       const item = db
         .prepare<
           [string],
-          { product_id: string; count_original: number; count_last_audit: number | null }
+          { product_id: string; weight: number; last_audit_weight: number | null; count_original: number; count_last_audit: number | null }
         >(
-          `SELECT product_id, count_original, count_last_audit FROM inventory_items WHERE id = ?`,
+          `SELECT product_id, weight, last_audit_weight, count_original, count_last_audit FROM inventory_items WHERE id = ?`,
         )
         .get(itemId);
       if (!item) continue;
 
-      const prev = item.count_last_audit ?? item.count_original;
+      const product = db
+        .prepare<[string], { kind: string }>(`SELECT kind FROM products WHERE id = ?`)
+        .get(item.product_id);
+      const isDiscrete = product?.kind === "discrete";
+
+      const prev = isDiscrete
+        ? item.count_last_audit ?? item.count_original
+        : item.last_audit_weight ?? item.weight;
+
       db.prepare(
         `INSERT INTO audits (inventory_id, date, mode, value, prev_value, confirmed_by)
          VALUES (?, ?, 'presence', ?, ?, 'bin-check')`,
       ).run(itemId, date, prev, prev);
+      if (isDiscrete) {
         db.prepare(
           `UPDATE inventory_items SET count_last_audit = ? WHERE id = ?`,
         ).run(prev, itemId);
       }
+    }
 
     for (const itemId of goneItemIds) {
       try {