feat(trade-executor): defer outside_market_hours signals to next open

Kevin's signals are mid-long term (weeks/months) and he uploads almost
exclusively pre-market or evenings. Before this change, every such
signal hit RiskManager.outside_market_hours, got consumed off the
Redis stream, and was lost. End result: 71 emitted signals, 0 trades.

New behaviour: when RiskManager rejects with outside_market_hours,
push the signal into a Redis sorted-set keyed by next_market_open
(via Alpaca's clock API — handles weekends + holidays). A background
drain task polls the set every kevin_defer_drain_interval_s (60s);
any signal whose target <= now gets re-run through process_signal.

Safety:
  - kevin_max_defer_hours (default 72h) caps signal staleness so we
    don't trade on week-old views.
  - Other RiskManager rejections (cooldown, kill-switch, drawdown
    halt) fall through to the existing drop path.
  - kevin_defer_outside_market_hours toggle defaults True; flip to
    false for legacy behaviour.

Slack: new notify_deferred() emits "🕒 Meet Kevin: DEFERRED
NVDA until Mon 13:30 UTC (market closed; conviction 0.85)" instead
of the noisy outside_market_hours rejection spam.

Tests: 5 queue + 4 integration = 9 new, all 32 trade-executor tests
GREEN.

tests/services/trade_executor/test_defer_integration.py

@@ -0,0 +1,138 @@
+"""process_signal integration: defer outside_market_hours instead of dropping."""
+
+from __future__ import annotations
+
+from datetime import datetime, timedelta, timezone
+from decimal import Decimal
+from unittest.mock import AsyncMock, MagicMock, patch
+from uuid import uuid4
+
+import fakeredis.aioredis
+import pytest
+
+from services.trade_executor.config import TradeExecutorConfig
+from services.trade_executor.deferred_queue import DeferredSignalQueue
+from services.trade_executor.main import process_signal
+from shared.schemas.trading import SignalDirection, TradeSignal
+
+
+@pytest.fixture
+def cfg() -> TradeExecutorConfig:
+    return TradeExecutorConfig(
+        kevin_defer_outside_market_hours=True,
+        kevin_max_defer_hours=72.0,
+        kevin_defer_drain_interval_s=60,
+        alpaca_api_key="t",
+        alpaca_secret_key="t",
+    )
+
+
+@pytest.fixture
+async def queue():
+    r = fakeredis.aioredis.FakeRedis()
+    try:
+        yield DeferredSignalQueue(r)
+    finally:
+        await r.aclose()
+
+
+def _signal(age_hours: float = 0.0) -> TradeSignal:
+    return TradeSignal(
+        signal_id=uuid4(),
+        ticker="NVDA",
+        direction=SignalDirection.LONG,
+        strength=0.8,
+        strategy_sources=["meet_kevin:buy:0.8"],
+        timestamp=datetime.now(timezone.utc) - timedelta(hours=age_hours),
+        target_dollars=Decimal("2000"),
+    )
+
+
+def _counters():
+    return {
+        "trades_executed": MagicMock(),
+        "rejections": MagicMock(),
+        "fill_latency": MagicMock(),
+    }
+
+
+async def test_outside_market_hours_signal_is_deferred(cfg, queue):
+    rm = MagicMock()
+    rm.check_risk = AsyncMock(return_value=(False, "outside_market_hours"))
+    broker = MagicMock()
+    next_open = datetime.now(timezone.utc) + timedelta(hours=12)
+    with patch(
+        "services.trade_executor.main._next_market_open",
+        AsyncMock(return_value=next_open),
+    ):
+        await process_signal(
+            _signal(),
+            rm,
+            broker,
+            publisher=AsyncMock(),
+            counters=_counters(),
+            db_session_factory=None,
+            slack_notifier=None,
+            deferred_queue=queue,
+            config=cfg,
+        )
+    assert await queue.size() == 1
+
+
+async def test_stale_signal_not_deferred(cfg, queue):
+    """Signal older than max_defer_hours falls through to normal rejection."""
+    cfg = cfg.model_copy(update={"kevin_max_defer_hours": 24.0})
+    rm = MagicMock()
+    rm.check_risk = AsyncMock(return_value=(False, "outside_market_hours"))
+    with patch(
+        "services.trade_executor.main._next_market_open",
+        AsyncMock(return_value=datetime.now(timezone.utc) + timedelta(hours=12)),
+    ):
+        await process_signal(
+            _signal(age_hours=48),  # 48h > 24h cap
+            rm,
+            broker=MagicMock(),
+            publisher=AsyncMock(),
+            counters=_counters(),
+            db_session_factory=None,
+            slack_notifier=None,
+            deferred_queue=queue,
+            config=cfg,
+        )
+    assert await queue.size() == 0
+
+
+async def test_non_market_hours_rejection_not_deferred(cfg, queue):
+    """Other rejections (e.g. cooldown, kill switch) don't defer."""
+    rm = MagicMock()
+    rm.check_risk = AsyncMock(return_value=(False, "cooldown_active (5m remaining)"))
+    await process_signal(
+        _signal(),
+        rm,
+        broker=MagicMock(),
+        publisher=AsyncMock(),
+        counters=_counters(),
+        db_session_factory=None,
+        slack_notifier=None,
+        deferred_queue=queue,
+        config=cfg,
+    )
+    assert await queue.size() == 0
+
+
+async def test_defer_disabled_falls_through(cfg, queue):
+    cfg = cfg.model_copy(update={"kevin_defer_outside_market_hours": False})
+    rm = MagicMock()
+    rm.check_risk = AsyncMock(return_value=(False, "outside_market_hours"))
+    await process_signal(
+        _signal(),
+        rm,
+        broker=MagicMock(),
+        publisher=AsyncMock(),
+        counters=_counters(),
+        db_session_factory=None,
+        slack_notifier=None,
+        deferred_queue=queue,
+        config=cfg,
+    )
+    assert await queue.size() == 0