feat(V2): shared Candle validator + uniform 'candles' response key

Introduce common/candles.py with a Pydantic Candle model enforcing OHLC
consistency (high≥max, low≤min), non-negative volume and positive
timestamp. validate_candles() coerces upstream rows, sorts by timestamp
and raises HTTPException(502) on malformed data — surfacing upstream
data corruption as a retryable envelope instead of silently returning
nonsense.

Wired into all five exchange historical endpoints (Bybit, Hyperliquid,
Deribit, Alpaca, IBKR). BREAKING: Alpaca get_bars and IBKR get_bars now
return 'candles' (was 'bars') to align with the other exchanges.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/unit/common/test_candles.py

@@ -0,0 +1,72 @@
+from __future__ import annotations
+
+import pytest
+from cerbero_mcp.common.candles import Candle, validate_candles
+from fastapi import HTTPException
+
+
+def test_valid_candle():
+    c = Candle(timestamp=1_700_000_000_000, open=100.0, high=110.0,
+               low=95.0, close=105.0, volume=12.5)
+    assert c.high == 110.0
+
+
+def test_high_below_close_rejected():
+    with pytest.raises(ValueError):
+        Candle(timestamp=1, open=100, high=90, low=80, close=95, volume=1)
+
+
+def test_high_below_open_rejected():
+    with pytest.raises(ValueError):
+        Candle(timestamp=1, open=100, high=90, low=80, close=85, volume=1)
+
+
+def test_low_above_close_rejected():
+    with pytest.raises(ValueError):
+        Candle(timestamp=1, open=100, high=110, low=105, close=102, volume=1)
+
+
+def test_low_above_open_rejected():
+    with pytest.raises(ValueError):
+        Candle(timestamp=1, open=95, high=110, low=100, close=105, volume=1)
+
+
+def test_negative_volume_rejected():
+    with pytest.raises(ValueError):
+        Candle(timestamp=1, open=100, high=110, low=90, close=105, volume=-1)
+
+
+def test_non_positive_timestamp_rejected():
+    with pytest.raises(ValueError):
+        Candle(timestamp=0, open=100, high=110, low=90, close=105, volume=1)
+
+
+def test_validate_candles_sorts_by_timestamp():
+    raw = [
+        {"timestamp": 3, "open": 1, "high": 2, "low": 1, "close": 1, "volume": 0},
+        {"timestamp": 1, "open": 1, "high": 2, "low": 1, "close": 1, "volume": 0},
+        {"timestamp": 2, "open": 1, "high": 2, "low": 1, "close": 1, "volume": 0},
+    ]
+    out = validate_candles(raw)
+    assert [c["timestamp"] for c in out] == [1, 2, 3]
+
+
+def test_validate_candles_coerces_string_numerics():
+    raw = [{"timestamp": "1", "open": "100", "high": "110",
+            "low": "90", "close": "105", "volume": "10"}]
+    out = validate_candles(raw)
+    assert out[0]["open"] == 100.0
+    assert isinstance(out[0]["volume"], float)
+
+
+def test_validate_candles_malformed_raises_http_502():
+    raw = [{"timestamp": 1, "open": 100, "high": 50, "low": 90,
+            "close": 105, "volume": 1}]
+    with pytest.raises(HTTPException) as exc_info:
+        validate_candles(raw)
+    assert exc_info.value.status_code == 502
+    assert "candle" in str(exc_info.value.detail).lower()
+
+
+def test_validate_candles_empty_list():
+    assert validate_candles([]) == []