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>

tests/unit/test_paper_trade_service.py

@@ -94,6 +94,7 @@ async def _add_bars(session, ticker_id: int, highs_lows: list[tuple[float, float
 
 
 async def test_resolve_closes_on_target(session):
+    await svc.set_exit_policy(session, mode="target")
     tid = await _seed(session, "AAA", close=100.0)
     trade = await svc.create_trade(session, 1, symbol="AAA", direction="long",
                                    entry_price=100.0, shares=10, stop_loss=95.0, target=110.0)
@@ -107,6 +108,7 @@ async def test_resolve_closes_on_target(session):
 
 
 async def test_resolve_closes_on_stop(session):
+    await svc.set_exit_policy(session, mode="target")
     tid = await _seed(session, "AAA", close=100.0)
     trade = await svc.create_trade(session, 1, symbol="AAA", direction="long",
                                    entry_price=100.0, shares=10, stop_loss=95.0, target=110.0)
@@ -118,6 +120,7 @@ async def test_resolve_closes_on_stop(session):
 
 
 async def test_resolve_leaves_open_when_neither_hit(session):
+    await svc.set_exit_policy(session, mode="target")
     tid = await _seed(session, "AAA", close=100.0)
     await svc.create_trade(session, 1, symbol="AAA", direction="long",
                            entry_price=100.0, shares=10, stop_loss=95.0, target=110.0)
@@ -171,3 +174,71 @@ async def test_alpha_short_and_missing_benchmark(session):
     row = (await svc.list_trades(session, 1, status="open"))[0]
     assert row["benchmark_return_pct"] == pytest.approx(0.0)
     assert row["alpha_pct"] == pytest.approx(10.0)
+
+
+def _b(d: date, hi: float, lo: float):
+    return svc.Bar(date=d, high=hi, low=lo)
+
+
+class TestTrailingClose:
+    def test_long_locks_gain(self):
+        # Runs to 120; the 12%-from-peak stop (120 → 105.6) is pierced on the drop.
+        bars = [_b(date(2026, 1, 2), 120, 110), _b(date(2026, 1, 3), 130, 100)]
+        hit = svc._trailing_close("long", 100.0, 95.0, 0.12, bars)
+        assert hit is not None
+        price, when, reason = hit
+        assert price == pytest.approx(105.6)
+        assert reason == "trailing"
+        assert when == date(2026, 1, 3)
+
+    def test_initial_stop_caps_loss(self):
+        bars = [_b(date(2026, 1, 2), 101, 94)]  # through the initial stop before running
+        hit = svc._trailing_close("long", 100.0, 95.0, 0.12, bars)
+        assert hit is not None
+        price, _, reason = hit
+        assert price == pytest.approx(95.0)
+        assert reason == "stop"
+
+    def test_none_when_neither_hit(self):
+        bars = [_b(date(2026, 1, 2), 105, 99), _b(date(2026, 1, 3), 106, 100)]
+        assert svc._trailing_close("long", 100.0, 95.0, 0.12, bars) is None
+
+
+async def test_exit_policy_defaults_and_round_trip(session):
+    assert await svc.get_exit_policy(session) == {"mode": "trailing", "trailing_pct": 12.0}
+    updated = await svc.set_exit_policy(session, mode="target", trailing_pct=15.0)
+    assert updated == {"mode": "target", "trailing_pct": 15.0}
+    assert (await svc.get_exit_policy(session))["mode"] == "target"
+
+
+async def test_exit_policy_rejects_bad_input(session):
+    with pytest.raises(ValidationError):
+        await svc.set_exit_policy(session, mode="bogus")
+    with pytest.raises(ValidationError):
+        await svc.set_exit_policy(session, trailing_pct=200.0)
+
+
+async def test_resolve_trailing_closes_with_reason(session):
+    tid = await _seed(session, "AAA", close=100.0)  # default policy: trailing 12%
+    await _add_open_trade(session, tid, "long", entry=100.0, shares=10, days_ago=10)
+    await _add_bars(session, tid, [(120, 110), (130, 100)], start=date.today())  # run up, pull back
+    assert await svc.resolve_open_trades(session) == 1
+    closed = await svc.list_trades(session, 1, status="closed")
+    assert closed[0]["close_reason"] == "trailing"
+
+
+async def test_manual_close_sets_reason(session):
+    await _seed(session, "AAA", close=112.0)
+    trade = await svc.create_trade(session, 1, symbol="AAA", direction="long",
+                                   entry_price=100.0, shares=5, stop_loss=95.0, target=120.0)
+    await svc.close_trade(session, 1, trade.id)
+    assert (await svc.list_trades(session, 1, status="closed"))[0]["close_reason"] == "manual"
+
+
+async def test_list_open_exposes_trailing_stop(session):
+    tid = await _seed(session, "AAA", close=120.0)
+    await _add_open_trade(session, tid, "long", entry=100.0, shares=10, days_ago=10)
+    await _add_bars(session, tid, [(125, 118)], start=date.today())  # peak 125
+    row = (await svc.list_trades(session, 1, status="open"))[0]
+    assert row["trailing_stop"] == pytest.approx(110.0)  # 125 * (1 - 0.12)
+    assert row["trailing_distance_pct"] is not None