feat: consolidate ledger trade writes into portfolio_ledger

- add ledger consolidation migration and remove ledger_trades usage
- return portfolio state after v1 ledger trade writes
- deprecate legacy buy/sell endpoints with deprecation headers
- add BAT-016, DCY-006, and REQ-036~038 documentation
- update repository models and tests for unified ledger entries

tests/test_v1_portfolios_ledger.py

@@ -9,7 +9,7 @@ from unittest.mock import MagicMock, patch
 from fastapi.testclient import TestClient
 
 from app.core.config import Settings, get_settings
-from app.domain.models import LedgerTrade, Portfolio, TokenPrincipal
+from app.domain.models import LedgerEntry, Portfolio, TokenPrincipal
 from app.main import create_app
 
 _ENC_KEY = "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA="
@@ -55,7 +55,7 @@ def _make_portfolio(
     )
 
 
-def _make_trade(**kwargs) -> LedgerTrade:
+def _make_trade(**kwargs) -> LedgerEntry:
     defaults = dict(
         ledger_entry_id=1,
         portfolio_id=_PORTFOLIO_ID,
@@ -70,14 +70,14 @@ def _make_trade(**kwargs) -> LedgerTrade:
         recorded_at=datetime(2026, 5, 1, 1, 0, 0, tzinfo=timezone.utc),
     )
     defaults.update(kwargs)
-    return LedgerTrade(**defaults)
+    return LedgerEntry(**defaults)
 
 
 def _make_service_repo(
     *,
     daemon_id: str | None = _DAEMON_ID,
     portfolio: Portfolio | None = None,
-    trade: LedgerTrade | None = None,
+    trade: LedgerEntry | None = None,
     created: bool = True,
 ) -> MagicMock:
     repo = MagicMock()