fix(critical): remove dead manifold.get_probability() from legacy scan and fix BUY_NO payout calculation

- Legacy scan called ManifoldClient.get_probability(), removed in the v3
  matcher migration, causing AttributeError when positions had changed
  family keys. The block used Manifold to escalate positions to
  CLOSE_RECOMMENDED (inversion detection) — a trading decision forbidden
  under MANIFOLD_SIGNAL_ENABLED=false — so the dependency is removed
  entirely; the scan keeps family re-keying and sibling-conflict logic.

- PaperExecutor.close_position() computed cash += position_cost * resolution,
  ignoring direction: a winning BUY_NO (resolution=0.0) paid out $0 and
  reported a loss. Now settles per trade:
    BUY_YES: payout = shares * resolution
    BUY_NO:  payout = shares * (1 - resolution)
  with pnl = payout - net_cost; Telegram win/loss keys off pnl > 0.
  Adds read-only Database.get_open_trades_for_market().

- tests/test_paper_close.py covers the 4 deterministic payout cases;
  tests/conftest.py shims datetime.UTC for local Python 3.10 (prod is 3.11).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

bot/executor/paper.py

@@ -235,24 +235,49 @@ class PaperExecutor:
         """Close a paper position after market resolution.
 
         resolution: 1.0 if YES won, 0.0 if NO won.
-        Persists resolution and close_pnl to DB (computed via SQL from stored
-        entry_price and shares). Returns approximate P&L for logging.
+        Settlement payout per trade:
+          BUY_YES: shares * resolution
+          BUY_NO:  shares * (1 - resolution)
+        pnl = payout - net_cost.
+        Persists resolution and close_pnl to DB. Returns realized P&L for
+        logging, or None if no position is open.
         """
         if market_id not in self._portfolio.positions:
             return None
 
         position_cost = self._portfolio.positions.pop(market_id)
-        self._portfolio.cash += position_cost * resolution  # pay out winnings
+        open_trades = await self._db.get_open_trades_for_market(market_id)
+
+        if open_trades:
+            payout = sum(
+                float(t["shares"])
+                * (resolution if t["direction"] == "BUY_YES" else 1.0 - resolution)
+                for t in open_trades
+            )
+            net_cost = sum(float(t["net_cost"]) for t in open_trades)
+            pnl = payout - net_cost
+        else:
+            # In-memory position with no open DB trades: direction/shares are
+            # unknown, so settle at break-even instead of guessing the payout.
+            log.warning(
+                "close_position: no open DB trades for market %s — "
+                "settling at break-even", market_id,
+            )
+            payout = position_cost
+            pnl = 0.0
+
+        self._portfolio.cash += payout
 
         await self._db.close_paper_position(
             market_id,
             reason=f"market_resolved resolution={resolution:.1f}",
             resolution=resolution,
         )
-        approx_pnl = position_cost * resolution - position_cost
-        log.info("Closed position in %s, resolution=%.1f", market_id, resolution)
-        asyncio.create_task(
-            telegram.trade_closed(question or market_id, approx_pnl)
+        log.info(
+            "Closed position in %s, resolution=%.1f payout=$%.2f pnl=%+.2f",
+            market_id, resolution, payout, pnl,
         )
-        # Approximate PnL: settlement value minus cost. Exact value is in close_pnl.
-        return approx_pnl
+        asyncio.create_task(
+            telegram.trade_closed(question or market_id, pnl)
+        )
+        return pnl