feat(V2): builder client centralizzato (solo deribit per ora)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/cerbero_mcp/exchanges/__init__.py

@@ -0,0 +1,22 @@
+"""Builder centralizzato di client per ClientRegistry."""
+from __future__ import annotations
+
+from typing import Literal
+
+from cerbero_mcp.settings import Settings
+
+Environment = Literal["testnet", "mainnet"]
+
+
+async def build_client(
+    settings: Settings, exchange: str, env: Environment
+):
+    if exchange == "deribit":
+        from cerbero_mcp.exchanges.deribit.client import DeribitClient
+
+        return DeribitClient(
+            client_id=settings.deribit.client_id,
+            client_secret=settings.deribit.client_secret.get_secret_value(),
+            testnet=(env == "testnet"),
+        )
+    raise ValueError(f"unsupported exchange: {exchange}")