feat(V2): unified /mcp interface; retire Bybit/Alpaca to old/

Add a common cross-exchange interface (/mcp) over the integrated venues
(deribit, hyperliquid):

- get_instruments: uniform schema where each row carries its own
  `exchange`, `fees` (maker/taker, live from Deribit, null where the
  venue has no per-instrument schedule) and `history_start` (listing
  date, live from Deribit creation_timestamp), plus type/tick_size and a
  lossless `native` blob. Optional `exchange` filter; fan-out otherwise.
- get_historical: generalized to {exchange, instrument, interval,
  start_date, end_date}, returning a single chosen venue's candles.
  Consensus merge stays available on /mcp-cross.

New: routers/unified.py, exchanges/cross/instruments.py (normalizers),
UnifiedClient in cross/client.py, schemas in cross/tools.py. Deribit
get_instruments now also surfaces maker/taker_commission and
creation_timestamp (additive).

Retire Bybit and Alpaca from the API surface: move clients, routers,
settings classes and their tests under old/ (history preserved via
git mv); drop them from the builder, /mcp-cross dispatch and symbol_map.
Bybit remains a public funding/OI data source in sentiment (not the
trading client). IBKR is intentionally excluded from /mcp for now.

Docs: rewrite API_REFERENCE.md (remove Bybit/Alpaca, document /mcp,
clarify that data_timestamp is injected globally by middleware).

Tests: add unified-interface coverage; update cross/settings/builder/boot
tests for the reduced venue set. Fix a pre-existing flaky assertion in
the Hyperliquid signing test (r/s use eth_utils.to_hex like the official
SDK, so a leading zero byte yields <66 chars ~1/256 of the time).

323 passed, ruff clean.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/unit/exchanges/cross/test_client.py

@@ -20,12 +20,6 @@ class _Fake:
         self.calls.append(kwargs)
         return {"candles": list(self._candles)}
 
-    async def get_bars(self, **kwargs: Any) -> dict[str, Any]:
-        if self._raises:
-            raise self._raises
-        self.calls.append(kwargs)
-        return {"candles": list(self._candles)}
-
 
 class _FakeRegistry:
     def __init__(self, clients: dict[str, _Fake]):
@@ -43,9 +37,8 @@ def _c(ts: int, close: float = 100.0) -> dict[str, Any]:
 
 
 @pytest.mark.asyncio
-async def test_crypto_three_sources_aggregates():
+async def test_crypto_two_sources_aggregates():
     fakes = {
-        "bybit":       _Fake([_c(1, 100), _c(2, 200)]),
         "hyperliquid": _Fake([_c(1, 100), _c(2, 200)]),
         "deribit":     _Fake([_c(1, 100), _c(2, 200)]),
     }
@@ -57,16 +50,15 @@ async def test_crypto_three_sources_aggregates():
     assert out["symbol"] == "BTC"
     assert out["asset_class"] == "crypto"
     assert len(out["candles"]) == 2
-    assert out["candles"][0]["sources"] == 3
+    assert out["candles"][0]["sources"] == 2
     assert out["candles"][0]["div_pct"] == 0.0
-    assert set(out["sources_used"]) == {"bybit", "hyperliquid", "deribit"}
+    assert set(out["sources_used"]) == {"hyperliquid", "deribit"}
     assert out["failed_sources"] == []
 
 
 @pytest.mark.asyncio
 async def test_crypto_partial_failure_returns_partial_with_warning():
     fakes = {
-        "bybit":       _Fake([_c(1, 100)]),
         "hyperliquid": _Fake([_c(1, 100)]),
         "deribit":     _Fake(raises=RuntimeError("upstream down")),
     }
@@ -75,8 +67,8 @@ async def test_crypto_partial_failure_returns_partial_with_warning():
         symbol="BTC", asset_class="crypto", interval="1h",
         start_date="2026-05-09T00:00:00", end_date="2026-05-10T00:00:00",
     )
-    assert out["candles"][0]["sources"] == 2
-    assert set(out["sources_used"]) == {"bybit", "hyperliquid"}
+    assert out["candles"][0]["sources"] == 1
+    assert set(out["sources_used"]) == {"hyperliquid"}
     assert len(out["failed_sources"]) == 1
     assert out["failed_sources"][0]["exchange"] == "deribit"
     assert "upstream down" in out["failed_sources"][0]["error"]
@@ -85,7 +77,6 @@ async def test_crypto_partial_failure_returns_partial_with_warning():
 @pytest.mark.asyncio
 async def test_all_sources_fail_raises_502():
     fakes = {
-        "bybit":       _Fake(raises=RuntimeError("a")),
         "hyperliquid": _Fake(raises=RuntimeError("b")),
         "deribit":     _Fake(raises=RuntimeError("c")),
     }
@@ -109,20 +100,6 @@ async def test_unsupported_symbol_raises_400():
     assert exc_info.value.status_code == 400
 
 
-@pytest.mark.asyncio
-async def test_stocks_routes_to_alpaca_only():
-    fake = _Fake([_c(1, 175.0)])
-    cc = CrossClient(_FakeRegistry({"alpaca": fake}), env="mainnet")
-    out = await cc.get_historical(
-        symbol="AAPL", asset_class="stocks", interval="1d",
-        start_date="2026-04-09T00:00:00", end_date="2026-04-10T00:00:00",
-    )
-    assert out["sources_used"] == ["alpaca"]
-    assert out["candles"][0]["close"] == 175.0
-    # Alpaca was called with native symbol
-    assert fake.calls[0]["symbol"] == "AAPL"
-
-
 @pytest.mark.asyncio
 async def test_unsupported_interval_raises_400():
     cc = CrossClient(_FakeRegistry({}), env="mainnet")