feat(kevin): correct exits, realized P&L, wire exit scanner

- executor: EXIT/SELL signals close the FULL held broker position (not a target_dollars-sized fresh order) and skip when flat

- executor: book realized P&L on the closing trade ((fill - avg_entry)*qty) so the dashboard P&L + win-rate populate; entries leave pnl=None

- exit scanner: wired into the bridge run loop on kevin_bridge_exit_scan_cron (daily ET gate; croniter intentionally not a dependency) plus an offsetting-SELL guard so it only emits exits for currently-held tickers

[ci skip]

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

services/kevin_signal_bridge/exit_scanner.py

@@ -27,15 +27,26 @@ class ExitScanner:
         session_factory: Callable[..., Any],
         publisher: Any,
         config: Any,
+        broker: Any,
     ) -> None:
         self.session_factory = session_factory
         self.publisher = publisher
         self.config = config
+        self.broker = broker
 
     async def scan_and_emit_exits(self) -> int:
         """Returns the number of EXIT signals emitted."""
         now = datetime.now(timezone.utc)
         emitted = 0
+
+        # Offsetting-SELL guard: only emit exits for tickers STILL held at the
+        # broker, so we never re-emit for an already-closed position. With zero
+        # open positions this set is empty → the scan is a safe no-op.
+        positions = await self.broker.get_positions()
+        held_tickers = {p.ticker for p in positions if p.qty != 0}
+        if not held_tickers:
+            return 0
+
         async with self.session_factory() as session:
             # Find open Kevin trades (FILLED, no closing trade yet on same ticker)
             open_trades = (
@@ -54,6 +65,9 @@ class ExitScanner:
             )
 
         for trade in open_trades:
+            # Skip tickers no longer held at the broker (already closed).
+            if trade.ticker not in held_tickers:
+                continue
             # Find the source audit row to learn the original holding_days target
             async with self.session_factory() as session:
                 audit = (