feat(portfolio): PortfolioLedger (alloc, equity/DD, persistenza+resume)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/portfolio/test_ledger.py

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+from pathlib import Path
+from src.portfolio.ledger import PortfolioLedger
+
+
+def test_alloc_split_by_weights(tmp_path):
+    L = PortfolioLedger("PORTX", total_capital=1000.0, data_dir=tmp_path)
+    alloc = L.allocate({"a": 0.6, "b": 0.4})
+    assert alloc == {"a": 600.0, "b": 400.0}
+
+
+def test_update_tracks_equity_and_dd(tmp_path):
+    L = PortfolioLedger("PORTX", total_capital=1000.0, data_dir=tmp_path)
+    L.update_equity({"a": 700.0, "b": 500.0})
+    assert L.equity == 1200.0 and L.peak == 1200.0 and L.max_dd == 0.0
+    L.update_equity({"a": 500.0, "b": 400.0})
+    assert L.equity == 900.0
+    assert abs(L.max_dd - 25.0) < 1e-9
+
+
+def test_persist_and_resume(tmp_path):
+    L = PortfolioLedger("PORTX", total_capital=1000.0, data_dir=tmp_path)
+    L.update_equity({"a": 1100.0})
+    L.save()
+    L2 = PortfolioLedger("PORTX", total_capital=1000.0, data_dir=tmp_path)
+    assert L2.equity == 1100.0 and L2.peak == 1100.0
+    assert (tmp_path / "PORTX" / "equity.jsonl").exists()