fix(backtest): flag a lookback the recommendation was not computed on

Selecting a different window or a comparison strategy silently made the tiles
stop matching the recommendation below, which is baked into the report and
cannot follow a dropdown. On load they now agree by construction; moving off
that basis says so.

Also: an absent production row produced no headline and no benchmark, but any
passing gate finding still rendered a green "no warnings" chip — a success badge
for missing data, directly beside "this report predates the portfolio monitor".
Missing baseline now reads "baseline unavailable".

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

frontend/src/components/signals/BacktestPanel.tsx

@@ -42,8 +42,19 @@ export function BacktestPanel() {
   const monitor = report?.portfolio_monitor ?? null;
   const activeStrategy =
     selectedStrategy || monitor?.production_strategy || monitor?.strategies[0]?.strategy || '';
+  // Default to the window the recommendation was computed on, so the tiles and
+  // the recommendation never open showing different numbers. They used to: the
+  // backend preferred "all" while this defaulted to "3y". The 3y fallback is
+  // only for reports predating basis_lookback.
+  const basisLookback = report?.recommendation?.basis_lookback ?? null;
   const activeLookback =
-    selectedLookback || (monitor?.lookbacks.some((l) => l.lookback === '3y') ? '3y' : monitor?.lookbacks[0]?.lookback) || '';
+    selectedLookback ||
+    (basisLookback && monitor?.lookbacks.some((l) => l.lookback === basisLookback)
+      ? basisLookback
+      : monitor?.lookbacks.some((l) => l.lookback === '3y')
+        ? '3y'
+        : monitor?.lookbacks[0]?.lookback) ||
+    '';
   const monitorRun = useMemo(
     () =>
       monitor?.runs.find((row) => row.strategy === activeStrategy && row.lookback === activeLookback) ??
@@ -175,6 +186,9 @@ export function BacktestPanel() {
               activeLookback={activeLookback}
               onStrategyChange={setSelectedStrategy}
               onLookbackChange={setSelectedLookback}
+              basisLookback={basisLookback}
+              basisLookbackLabel={report.recommendation?.basis_lookback_label ?? null}
+              productionStrategy={monitor?.production_strategy ?? null}
             />
 
             {report.recommendation && (