fix: column layouts would not stick — five separate faults

1. A language change rebuilt the column defs, which sets the anti-clobber
   guard, but the effect that clears it listened to only two of the rebuild's
   causes. Guard stuck on → every column change was silently discarded for the
   rest of the session. Now keyed on the rebuilt defs themselves, so any future
   cause is covered.
2. The cluster grid had no guard at all: the same rebuild wrote its defaults
   over the saved layout, in the cache AND the database. Unrecoverable.
3. Worked-before and cluster read their state before the active profile was
   known, so they looked up the unscoped cache key (always a miss) and then
   saved under the scoped one. They now wait for the scope and remount on a
   profile switch, like the main log.
4. GetUIPref returns an ERROR, not "", while the settings store is not yet
   scoped — deliberately distinct from "unset". The frontend read it as "no
   preference", rendered defaults, and the first column event overwrote the
   good copy. It now retries instead of giving up.
5. The QSL manager had no storageKey, so it shared the main log's layout and
   each rewrote the other.

Also: the DB write is debounced (a resize drag fired dozens of writes) with a
flush on close, and a rejected write is retried rather than dropped.

frontend/src/components/RecentQSOsGrid.tsx

@@ -521,7 +521,13 @@ export function RecentQSOsGrid({ rows, myGrid, selectAllSignal, selectRowSignal,
     // Re-enable saving once AG Grid has settled the column events from the rebuild.
     const t = window.setTimeout(() => { restoringRef.current = false; }, 0);
     return () => window.clearTimeout(t);
-  }, [awardCols, awardShown]);
+    // Keyed on columnDefs ITSELF, not on the reasons it was rebuilt. Listing the
+    // causes here (awardCols/awardShown) missed the others — switching the UI
+    // language rebuilds the memo through `t`, which set restoringRef and left it
+    // set, so every column change for the rest of the session was silently
+    // discarded and the layout reverted on reload. Any future dependency of the
+    // memo is now covered for free.
+  }, [columnDefs]);
 
   function handleRowDoubleClicked(e: RowDoubleClickedEvent<QSOForm>) {
     if (e.data && onRowDoubleClicked) onRowDoubleClicked(e.data);