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>

app/routers/market.py

@@ -0,0 +1,21 @@
+"""Market-level endpoints (benchmark regime)."""
+
+from fastapi import APIRouter, Depends
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.dependencies import get_db, require_access
+from app.models.user import User
+from app.schemas.common import APIEnvelope
+from app.services.market_regime_service import get_market_regime
+
+router = APIRouter(tags=["market"])
+
+
+@router.get("/market/regime", response_model=APIEnvelope)
+async def market_regime(
+    _user: User = Depends(require_access),
+    db: AsyncSession = Depends(get_db),
+) -> APIEnvelope:
+    """Current benchmark (SPY) trend regime: bullish / bearish / neutral."""
+    data = await get_market_regime(db)
+    return APIEnvelope(status="success", data=data)