refactor(mcp-common): centralize base_url defaults in resolve_environment

Aggiunti kwargs opzionali default_base_url_live / default_base_url_testnet
a resolve_environment. Rimosse 8 chiamate creds.setdefault duplicate dai
4 servizi (alpaca, bybit, deribit, hyperliquid) ora passano gli URL
canonici direttamente al resolver.

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

services/mcp-deribit/src/mcp_deribit/__main__.py

@@ -27,15 +27,13 @@ def main():
     with open(creds_file) as f:
         creds = json.load(f)
 
-    # Default base URLs per backward-compat con secret schema legacy
-    creds.setdefault("base_url_live", "https://www.deribit.com/api/v2")
-    creds.setdefault("base_url_testnet", "https://test.deribit.com/api/v2")
-
     env_info = resolve_environment(
         creds,
         env_var="DERIBIT_TESTNET",
         flag_key="testnet",
         exchange="deribit",
+        default_base_url_live="https://www.deribit.com/api/v2",
+        default_base_url_testnet="https://test.deribit.com/api/v2",
     )
 
     client = DeribitClient(