momentum gate: long-only + wire the percentile onto live setups

Part 1 — long-only. The momentum edge is long top-momentum; the gate was
qualifying shorts on high-momentum names (fighting the trend), which showed as
the -0.13R Short(qual.) drag. While the gate is active, shorts no longer qualify
(backend qualification, backtest _momentum_qualifies, and the frontend mirror).

Part 2 — production wiring. Live setups now carry a real momentum rank, so the
dashboard, the Track Record's qualified stats, and outcome evaluation all gate on
the same value instead of deferring to floors:
- new momentum_service.compute_momentum_percentiles: 12-1 momentum per ticker,
  ranked across the universe into a {symbol: percentile} map.
- the daily R:R scan ranks the universe up front and stores each setup's
  percentile (new trade_setups.momentum_percentile column, migration 010).
- enhance_trade_setup mutates the same row, so the percentile is preserved;
  _trade_setup_to_dict + TradeSetupResponse expose it to the API.

Until a fresh scan runs, pre-existing setups have a null percentile and the gate
falls back to floors for them (longs) / excludes them (shorts) — they fill in on
the next scan. 341 backend tests pass; frontend build clean.

Needs the alembic upgrade (migration 010) on deploy.

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

app/schemas/trade_setup.py

@@ -48,4 +48,5 @@ class TradeSetupResponse(BaseModel):
     outcome_date: date | None = None
     evaluated_at: datetime | None = None
     current_price: float | None = None
+    momentum_percentile: float | None = None
     recommendation_summary: RecommendationSummaryResponse | None = None