feat(ui): simplify to 3-button manage layout and remove drawer grouping

db.js

@@ -266,6 +266,66 @@ function adjustQuantity(id, { newQuantity, delta, markOpened }) {
   return getItemById(id);
 }
 
+function addPacket(id, count = 1) {
+  const item = getItemById(id);
+  if (!item) return null;
+
+  const packSize = item.initial_quantity > 0 ? item.initial_quantity : 1;
+  const addedAmount = packSize * count;
+  const newQty = item.quantity + addedAmount;
+
+  const stmt = db.prepare(`
+    UPDATE items SET
+      quantity = ?,
+      updated_at = datetime('now', 'localtime')
+    WHERE id = ?
+  `);
+  stmt.run(newQty, id);
+
+  logActivity({
+    item_id: id,
+    item_name: item.name,
+    action: 'add_packet',
+    amount_change: addedAmount,
+    unit: item.unit,
+    note: `Added ${count} packet(s) (+${addedAmount} ${item.unit})`
+  });
+
+  return getItemById(id);
+}
+
+function removePacket(id, count = 1) {
+  const item = getItemById(id);
+  if (!item) return null;
+
+  const packSize = item.initial_quantity > 0 ? item.initial_quantity : 1;
+  const removeAmount = packSize * count;
+  let newQty = item.quantity - removeAmount;
+
+  if (newQty <= 0) {
+    newQty = 0;
+  }
+
+  const stmt = db.prepare(`
+    UPDATE items SET
+      quantity = ?,
+      updated_at = datetime('now', 'localtime')
+    WHERE id = ?
+  `);
+  stmt.run(newQty, id);
+
+  logActivity({
+    item_id: id,
+    item_name: item.name,
+    action: 'remove_packet',
+    amount_change: -removeAmount,
+    unit: item.unit,
+    note: `Removed ${count} packet(s) (-${removeAmount} ${item.unit})`
+  });
+
+  return getItemById(id);
+}
+
 function deleteItem(id) {
   const item = getItemById(id);
   if (!item) return false;
@@ -347,6 +407,8 @@ module.exports = {
   createItem,
   updateItem,
   adjustQuantity,
+  addPacket,
+  removePacket,
   deleteItem,
   getActivityLogs,
   getStats