fix: only count matured setups in the live track record

The outcome stats were dominated by quick stop-outs: near stops resolve as losses
within days while far targets take weeks, so a young sample (mostly pending,
0 expired) skewed sharply negative (e.g. 13.8% hit / -0.46R vs the backtest's
35.8% / +0.18R) — a maturation artifact, not a real result.

get_performance_stats now counts only setups whose full ~30-day window has
elapsed (_MATURITY_DAYS), so winners had as long as losers (unbiased, and
comparable to the backtest). A new `maturing` count reports the younger setups
held back. The Track Record UI relabels "Evaluated" -> "Matured", shows the
maturing count, and explains the window in the empty state + methodology note.

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

tests/unit/test_outcome_service.py

@@ -317,3 +317,26 @@ class TestGetPerformanceStats:
 
         stats = await get_performance_stats(db_session)
         assert stats["overall"]["total"] == 1
+
+    async def test_immature_setups_excluded_and_counted_as_maturing(self, db_session: AsyncSession):
+        ticker = await _make_ticker(db_session)
+        now = datetime.now(timezone.utc)
+        # Matured (detected well beyond the window) → counted in the stats.
+        db_session.add(_make_setup(
+            ticker, rr=2.0, actual_outcome=OUTCOME_TARGET_HIT, detected=now - timedelta(days=90),
+        ))
+        # Young but already resolved → excluded from stats, reported as maturing.
+        db_session.add(_make_setup(
+            ticker, rr=2.0, actual_outcome=OUTCOME_STOP_HIT, detected=now,
+        ))
+        # Young and still pending → also maturing.
+        db_session.add(_make_setup(ticker, detected=now))
+        await db_session.flush()
+
+        stats = await get_performance_stats(db_session)
+
+        assert stats["overall"]["total"] == 1   # only the matured win
+        assert stats["overall"]["wins"] == 1
+        assert stats["overall"]["hit_rate"] == 100.0
+        assert stats["pending"] == 1
+        assert stats["maturing"] == 2           # young resolved + pending