add market-regime guard (SPY trend) — inform + warn

New market_regime_service computes a benchmark (SPY) trend from its 50/200-day
SMAs, cached in a SystemSetting and refreshed by a nightly job; GET /market/regime
exposes it. Dashboard shows a regime banner; setup cards flag a counter-trend
caution when a setup fights the regime (LONG in a bearish market / SHORT in a
bullish one). Informational only — nothing is suppressed.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/pages/DashboardPage.tsx

@@ -4,6 +4,8 @@ import { useActivation } from '../hooks/useActivation';
 import { useTrades } from '../hooks/useTrades';
 import { useWatchlist } from '../hooks/useWatchlist';
 import { usePerformance } from '../hooks/usePerformance';
+import { useMarketRegime } from '../hooks/useMarketRegime';
+import { regimeColor, regimeDot, regimeHeadline } from '../lib/regime';
 import { Callout } from '../components/ui/Callout';
 import { Section } from '../components/ui/Section';
 import { SkeletonCard, SkeletonTable } from '../components/ui/Skeleton';
@@ -55,6 +57,7 @@ export default function DashboardPage() {
   const watchlist = useWatchlist();
   const activation = useActivation();
   const performance = usePerformance();
+  const regime = useMarketRegime();
 
   const qualifiedSetups = useMemo(
     () =>
@@ -98,6 +101,23 @@ export default function DashboardPage() {
         </h1>
       </div>
 
+      {/* Market regime banner */}
+      {regime.data && (
+        <div className="glass-sm flex items-center gap-2.5 px-4 py-2.5">
+          <span className={`inline-block h-2 w-2 rounded-full ${regimeDot(regime.data.label)}`} />
+          <span className="text-sm text-gray-400">Market regime:</span>
+          <span className={`text-sm font-semibold ${regimeColor(regime.data.label)}`}>
+            {regimeHeadline(regime.data)}
+          </span>
+          {regime.data.label === 'bearish' && (
+            <span className="text-xs text-gray-500">— be cautious on new longs</span>
+          )}
+          {regime.data.label === 'bullish' && (
+            <span className="text-xs text-gray-500">— shorts are counter-trend</span>
+          )}
+        </div>
+      )}
+
       {/* Metric strip */}
       {(trades.isLoading || performance.isLoading) ? (
         <div className="grid gap-4 sm:grid-cols-2 lg:grid-cols-4">