feat(V2): migrazione macro completa (read-only, env ignored)

- exchanges/macro: cot.py + cot_contracts.py + fetchers.py copiati 1:1 con
  rewrite import mcp_common -> cerbero_mcp.common, mcp_macro -> cerbero_mcp.exchanges.macro
- nuovo MacroClient stateless wrapper: trasporta solo fred_api_key/finnhub_api_key,
  niente HTTP session (i fetchers usano async_client ad-hoc)
- tools.py: 11 tool (get_treasury_yields, get_yield_curve_slope,
  get_breakeven_inflation, get_economic_indicators, get_macro_calendar,
  get_market_overview, get_equity_futures, get_asset_price, get_cot_tff,
  get_cot_disaggregated, get_cot_extreme_positioning) — niente write,
  niente leverage_cap
- routers/macro.py: prefix /mcp-macro, 11 route POST /tools/*
- builder branch macro: stesse credenziali per testnet/mainnet (env ignorato);
  registry istanzia 2 entry, costo trascurabile (wrapper stateless)
- test migrati: test_cot.py + test_fetchers.py (test_server_acl.py skippato V1-only)
- nuovo test test_build_client_macro_no_env_distinction in test_exchanges_builder.py

Suite: 224 passed.

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

src/cerbero_mcp/exchanges/__init__.py

@@ -44,4 +44,14 @@ async def build_client(
             secret_key=settings.alpaca.secret_key.get_secret_value(),
             paper=(env == "testnet"),
         )
+    if exchange == "macro":
+        # Read-only data provider — env ignored. Il registry
+        # istanzia comunque 2 entry (testnet/mainnet); costo trascurabile
+        # (wrapper stateless senza HTTP session).
+        from cerbero_mcp.exchanges.macro.client import MacroClient
+
+        return MacroClient(
+            fred_api_key=settings.macro.fred_api_key.get_secret_value(),
+            finnhub_api_key=settings.macro.finnhub_api_key.get_secret_value(),
+        )
     raise ValueError(f"unsupported exchange: {exchange}")