feat: ticker search, watchlist momentum column, alpha vs S&P 500

Three usability fixes:

1. Global ticker search in the sidebar (TickerSearch) — typeahead over the
   tracked universe that opens a ticker's detail page without adding it to the
   watchlist. Also wired into the mobile nav.

2. Watchlist table shows the ticker's 12-1 momentum percentile (the top-pick
   selector) instead of the noisy full S/R-level list. Enriched from the setup
   already loaded in watchlist_service._enrich_entry — no extra query.

3. Alpha vs the S&P 500 on paper trades (open + closed). New benchmark_prices
   table + benchmark_service store SPY daily closes (a standalone series, not a
   Ticker, so it never enters the scanner / momentum ranking / rankings) via a
   new daily-pipeline step. paper_trade_service computes per-trade
   benchmark_return / alpha_pct / alpha_usd over each holding period; the open-
   trades table, dashboard, and closed-trades panel surface per-trade and total
   alpha. The list read path never makes a provider call.

Deploy: alembic upgrade head, then run the benchmark/daily job once to populate
SPY closes (alpha shows "—" until then).

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

app/models/__init__.py

@@ -11,6 +11,7 @@ from app.models.settings import SystemSetting, IngestionProgress
 from app.models.alert import AlertLog
 from app.models.paper_trade import PaperTrade
 from app.models.regime_snapshot import RegimeSnapshot
+from app.models.benchmark_price import BenchmarkPrice
 
 __all__ = [
     "Ticker",
@@ -28,4 +29,5 @@ __all__ = [
     "AlertLog",
     "PaperTrade",
     "RegimeSnapshot",
+    "BenchmarkPrice",
 ]

app/models/benchmark_price.py

@@ -0,0 +1,25 @@
+from datetime import date as date_type
+
+from sqlalchemy import Date, Float, String, UniqueConstraint
+from sqlalchemy.orm import Mapped, mapped_column
+
+from app.database import Base
+
+
+class BenchmarkPrice(Base):
+    """Daily close for a benchmark index (e.g. SPY), used to compute trade alpha.
+
+    A standalone price series, deliberately NOT a tracked ``Ticker`` — so the
+    benchmark never enters the scanner, the momentum-percentile ranking, or the
+    rankings table. One row per (symbol, date).
+    """
+
+    __tablename__ = "benchmark_prices"
+    __table_args__ = (
+        UniqueConstraint("symbol", "date", name="uq_benchmark_symbol_date"),
+    )
+
+    id: Mapped[int] = mapped_column(primary_key=True)
+    symbol: Mapped[str] = mapped_column(String(20), nullable=False, index=True)
+    date: Mapped[date_type] = mapped_column(Date, nullable=False)
+    close: Mapped[float] = mapped_column(Float, nullable=False)