Riscrive `AlpacaClient` su `httpx.AsyncClient` rimuovendo ogni dipendenza
runtime da `alpaca-py`. 4 endpoint base distinti (trading paper/live,
stock data, crypto data, options data) gestiti via helper `_request`
con header `APCA-API-KEY-ID` / `APCA-API-SECRET-KEY`. Firma costruttore
e attributi pubblici (`paper`, `base_url`) invariati; `base_url` override
applica al solo trading endpoint. Nuovo `aclose()` per cleanup connessioni.
Test riscritti su `pytest-httpx` (29 test alpaca + leverage cap).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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>
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