Fix xAI sentiment: use Agent Tools web_search (Live Search deprecated)

xAI returned 410 — search_parameters/Live Search is retired. Route xAI
through the Responses API web_search tool instead (same path as OpenAI):
- OpenAISentimentProvider parametrized with base_url / tool_type / source
- xAI builds it against https://api.x.ai/v1 with the web_search tool
- Drop the dead Live Search code from the generic compatible provider
- Frontend label: "xAI Grok — web search"

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

app/services/sentiment_provider_service.py

@@ -39,12 +39,10 @@ PROVIDER_BASE_URLS: dict[str, str] = {
 }
 
 # Providers grounded in live web search. The rest score from model knowledge.
-# xAI grounds via Live Search (search_parameters); OpenAI/Gemini via their tools.
+# xAI and OpenAI ground via the Responses API web-search tool; Gemini via its
+# own search grounding.
 WEB_SEARCH_PROVIDERS = {"openai", "gemini", "xai"}
 
-# xAI Live Search: auto mode lets Grok search web + X when the query needs it.
-_XAI_SEARCH_PARAMETERS = {"mode": "auto", "return_citations": True}
-
 # Providers needing a user-supplied base URL (generic compatible endpoints).
 CUSTOM_BASE_URL_PROVIDERS = {"openai_compatible"}
 
@@ -181,16 +179,17 @@ async def build_sentiment_provider(db: AsyncSession):
     if provider == "gemini":
         from app.providers.gemini_sentiment import GeminiSentimentProvider
         return GeminiSentimentProvider(api_key, model)
-    if provider in {"deepseek", "xai", "openai_compatible"}:
+    if provider == "xai":
+        # xAI grounds via the Responses API web_search tool (the former Live
+        # Search / search_parameters API is deprecated).
+        from app.providers.openai_sentiment import OpenAISentimentProvider
+        return OpenAISentimentProvider(
+            api_key, model, base_url=base_url, tool_type="web_search", source="xai",
+        )
+    if provider in {"deepseek", "openai_compatible"}:
         if not base_url:
             raise ProviderError(f"No base_url configured for sentiment provider '{provider}'")
         from app.providers.openai_compatible_sentiment import OpenAICompatibleSentimentProvider
-        if provider == "xai":
-            return OpenAICompatibleSentimentProvider(
-                api_key, model, base_url, source="xai",
-                live_search=True,
-                extra_body={"search_parameters": _XAI_SEARCH_PARAMETERS},
-            )
         return OpenAICompatibleSentimentProvider(api_key, model, base_url, source=provider)
 
     raise ProviderError(f"Unsupported sentiment provider '{provider}'")