feat: trailing-stop auto-exit for paper trades + close/digest alerts

Applies the backtest-validated trailing stop to live paper trading, and surfaces
it transparently.

Exit (A):
- New paper-trade exit policy (paper_exit_mode=trailing, paper_trailing_pct=12),
  tunable in Admin → Paper-Trade Exit. resolve_open_trades runs a trailing stop
  (initial stop as floor, ratchets up from the peak; target ignored — the
  validated rule) and records close_reason (trailing|stop|target|manual; +migration
  013).
- list_trades enriches open trades with the live trailing-stop level + distance %.
  Open Trades panel shows the active tactic and a Trail Stop column.

Alerts (B):
- Daily digest now lists open trades with unrealized gain, trailing stop, and how
  far away it is.
- New "trade closed" alert: one summary per auto-close (trailing/target/stop, not
  manual) — direction, reason, days held, P&L abs+%/R — covering wins AND
  stop-loss losses. Deduped by trade id; toggle in Admin alerts.

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

frontend/src/components/admin/AlertSettings.tsx

@@ -13,14 +13,16 @@ type TriggerKey =
   | 'sr_proximity_enabled'
   | 'score_drop_enabled'
   | 'digest_enabled'
-  | 'regime_quadrant_enabled';
+  | 'regime_quadrant_enabled'
+  | 'trade_closed_enabled';
 
 const TRIGGERS: { key: TriggerKey; label: string; hint: string }[] = [
   { key: 'qualified_enabled', label: 'Qualified setups', hint: 'a setup newly clears the activation gate' },
   { key: 'sr_proximity_enabled', label: 'Watchlist S/R proximity', hint: 'a watched ticker nears a strong support/resistance' },
   { key: 'score_drop_enabled', label: 'Score deterioration', hint: 'a watched ticker’s composite drops sharply' },
-  { key: 'digest_enabled', label: 'Daily digest', hint: 'one end-of-day summary of qualified setups' },
+  { key: 'digest_enabled', label: 'Daily digest', hint: 'end-of-day summary incl. open trades + trailing stops' },
   { key: 'regime_quadrant_enabled', label: 'Regime quadrant change', hint: 'the regime monitor shifts quadrant (hysteresis + cooldown)' },
+  { key: 'trade_closed_enabled', label: 'Trade closed', hint: 'a paper trade auto-closes (trailing/target/stop) — incl. losses' },
 ];
 
 function Toggle({ checked, onChange, label, hint }: {
@@ -59,6 +61,7 @@ export function AlertSettings() {
     score_drop_enabled: true,
     digest_enabled: true,
     regime_quadrant_enabled: true,
+    trade_closed_enabled: true,
   });
 
   useEffect(() => {
@@ -71,6 +74,7 @@ export function AlertSettings() {
         score_drop_enabled: data.score_drop_enabled,
         digest_enabled: data.digest_enabled,
         regime_quadrant_enabled: data.regime_quadrant_enabled,
+        trade_closed_enabled: data.trade_closed_enabled,
       });
     }
   }, [data]);