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/BacktestRecommendationCard.tsx

@@ -81,7 +81,16 @@ export function BacktestRecommendationCard({
       <div className="glass border border-blue-400/20 p-4">
         <div className="flex flex-wrap items-center justify-between gap-2">
           <p className="section-index">What this backtest recommends</p>
-          {warningCount > 0 ? (
+          {/* No headline means the backend found no production monitor row, so
+              nothing here describes the production book. Zero keyword warnings
+              is then absence of data, not a clean bill of health — a green chip
+              beside "this report predates the portfolio monitor" would be a
+              success badge for missing data. */}
+          {!recommendation.headline ? (
+            <span className="rounded-full border border-white/15 bg-white/[0.05] px-2 py-0.5 text-[10px] font-semibold uppercase tracking-wider text-gray-400">
+              baseline unavailable
+            </span>
+          ) : warningCount > 0 ? (
             <span className="rounded-full border border-amber-400/40 bg-amber-400/10 px-2 py-0.5 text-[10px] font-semibold uppercase tracking-wider text-amber-300">
               ⚠ {warningCount} warning{warningCount > 1 ? 's' : ''}
             </span>