fix(ui): make item description a drag-resizable textarea (rows + resize:vertical) across invoice/order/offer

Replaces MUI autosize (no handle, mis-wraps in table cells) with a fixed 2-row textarea + resize:vertical so the box wraps and the user can drag it taller. Restores the dead '& input' sx as '& textarea'.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/admin/pages/OfferDetail.tsx

@@ -308,8 +308,8 @@ function SortableItemRow({
           placeholder="Volitelný"
           InputProps={{ readOnly }}
           multiline
-          minRows={1}
-          maxRows={8}
+          rows={2}
+          sx={{ "& textarea": { resize: "vertical" } }}
         />
         <Box
           sx={{
@@ -421,9 +421,14 @@ function SortableItemRow({
             placeholder="Podrobný popis (volitelný)"
             InputProps={{ readOnly }}
             multiline
-            minRows={1}
-            maxRows={8}
-            sx={{ "& input": { fontSize: "0.8rem", opacity: 0.8 } }}
+            rows={2}
+            sx={{
+              "& textarea": {
+                fontSize: "0.8rem",
+                opacity: 0.8,
+                resize: "vertical",
+              },
+            }}
           />
         </Box>
       </TableCell>