fix(downloads): fix column sync bugs + simplify component

- Fix localStorage key format (use hook's setColumnsOrder/setMultipleColumnWidths)
- Fix columnsWidth read shape (object-keyed entries, not {accessor,width})
- Safe JSON.parse with try/catch fallback
- Per-widget storeKey (include itemId, sort columns)
- Reset initialSyncDone on storeKey change
- Remove forced table-layout:fixed (fights resize lifecycle)
- Skip persist until initial server restore completes
- Extract helpers and lookup tables (code-simplifier)

packages/widgets/src/downloads/styles.css

@@ -11,10 +11,6 @@
   background-color: transparent !important;
 }
 
-.downloads-table .mantine-datatable-table {
-  table-layout: fixed;
-}
-
 .downloads-table .mantine-datatable-table tr {
   background-color: transparent;
 }