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

docs/batches/bat-016_20260605_ledger-accounting-consolidation/verification.md

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+# BAT-016 Verification
+
+- Status: passed
+- Batch: BAT-016
+
+## Acceptance Mapping
+- REQ-036:
+  - AC-1~3: `ledger_trades` application references removed; new migration `20260605_0025_ledger_consolidation.py` and `ensure_schema()` consolidate trade columns into `portfolio_ledger`.
+  - AC-4~5: repository write/read path uses `portfolio_ledger`; recent trade mapping is `LedgerEntry`-based.
+  - AC-6~7: full regression passes under the project venv.
+- REQ-037:
+  - AC-1~2: `POST /v1/portfolios/{portfolio_id}/ledger/trades` is the authoritative trade write endpoint.
+  - AC-3~5: response includes `ledger_entry_id`, `order_id`, `execution_id`, `side`, `fee_amount`, `tax_amount`, `cash_balance_after`, and `asset_quantity_after`.
+  - AC-6: duplicate broker identifiers are resolved via repository idempotency lookup.
+  - AC-7: tests cover buy/sell, negative asset quantity, duplicate request behavior, and response state fields.
+- REQ-038:
+  - AC-1~2: legacy buy/sell route decorators use `deprecated=True`.
+  - AC-3~4: legacy buy/sell responses/errors emit `Deprecation: true`; `tests/test_auth.py::test_legacy_buy_sell_routes_emit_deprecation_header` verifies this behavior.
+
+## Evidence
+- Test:
+  - `.venv/bin/python -m pytest -q tests/test_domain_services.py tests/test_v1_portfolios_ledger.py tests/test_daemon_assignment.py tests/test_v1.py`
+  - Result: `47 passed in 3.66s`
+  - `.venv/bin/python -m pytest -q`
+  - Result: `373 passed, 3 warnings in 14.78s`
+- Manual:
+  - Confirmed legacy routes return `Deprecation: true` using `TestClient` with `PORTFOLIOHUB_DB_ENABLED=false` and trade-write token.
+  - Confirmed app code no longer contains `LedgerTrade`; only transitional schema-cleanup references remain for dropping old `ledger_trades`/`action` structures.
+- Logs:
+  - Full pytest output captured in terminal execution.
+
+## Result
+- Ready for Release: true
+- Blocking Issues: none