feat(V2): migrazione alpaca completa

Task 6.7: porting alpaca da services/mcp-alpaca a src/cerbero_mcp.
client.py + leverage_cap.py copiati 1:1 (default cap 1 cash).
tools.py: 17 tool senza ACL/Principal/audit. Router /mcp-alpaca con 18
route (env_info + 17 tool). Builder branch alpaca: paper=(env=="testnet"),
api_key viene da settings.alpaca.api_key_id. Test client + leverage_cap
migrati (15 test alpaca pass). Test builder con stub SDK alpaca-py.

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

tests/unit/test_exchanges_builder.py

@@ -71,6 +71,37 @@ async def test_build_client_hyperliquid_returns_correct_env(monkeypatch):
     assert "test" not in c_live.base_url.lower()
 
 
+@pytest.mark.asyncio
+async def test_build_client_alpaca_returns_correct_env(monkeypatch):
+    from tests.unit.test_settings import _minimal_env
+
+    for k, v in _minimal_env().items():
+        monkeypatch.setenv(k, v)
+
+    # Stub alpaca SDK clients per evitare connessioni reali in __init__
+    from cerbero_mcp.exchanges.alpaca import client as alpaca_client
+
+    class _FakeSdk:
+        def __init__(self, **kwargs):
+            self.kwargs = kwargs
+
+    monkeypatch.setattr(alpaca_client, "TradingClient", _FakeSdk)
+    monkeypatch.setattr(alpaca_client, "StockHistoricalDataClient", _FakeSdk)
+    monkeypatch.setattr(alpaca_client, "CryptoHistoricalDataClient", _FakeSdk)
+    monkeypatch.setattr(alpaca_client, "OptionHistoricalDataClient", _FakeSdk)
+
+    from cerbero_mcp.settings import Settings
+    from cerbero_mcp.exchanges import build_client
+
+    s = Settings()
+    c_test = await build_client(s, "alpaca", "testnet")
+    c_live = await build_client(s, "alpaca", "mainnet")
+
+    assert c_test is not c_live
+    assert c_test.paper is True
+    assert c_live.paper is False
+
+
 @pytest.mark.asyncio
 async def test_build_client_unknown_exchange_raises(monkeypatch):
     from tests.unit.test_settings import _minimal_env