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

- exchanges/sentiment/{client,fetchers,tools}.py: SentimentClient wrapper stateless (cryptopanic_key, lunarcrush_key)
- routers/sentiment.py: 9 tool POST sotto /mcp-sentiment (news, social, funding, OI, liquidations, cointegration)
- exchanges/__init__.py: branch builder per sentiment (env ignored)
- tests/unit/exchanges/sentiment: migrato test_fetchers, scartato test_server_acl V1-only
- tests/unit/test_exchanges_builder.py: aggiunto test_build_client_sentiment_no_env_distinction
- fetchers.py: env var lookup allineato a LUNARCRUSH_KEY (con fallback LUNARCRUSH_API_KEY)

241 test passano.

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

src/cerbero_mcp/exchanges/__init__.py

@@ -54,4 +54,13 @@ async def build_client(
             fred_api_key=settings.macro.fred_api_key.get_secret_value(),
             finnhub_api_key=settings.macro.finnhub_api_key.get_secret_value(),
         )
+    if exchange == "sentiment":
+        # Read-only data provider — env ignored (CryptoPanic, LunarCrush e
+        # endpoint pubblici di funding/OI multi-exchange sono unici).
+        from cerbero_mcp.exchanges.sentiment.client import SentimentClient
+
+        return SentimentClient(
+            cryptopanic_key=settings.sentiment.cryptopanic_key.get_secret_value(),
+            lunarcrush_key=settings.sentiment.lunarcrush_key.get_secret_value(),
+        )
     raise ValueError(f"unsupported exchange: {exchange}")