fix(research): remove Grounded from LLM call — incompatible with JSONSchema in Gemini API

Gemini rejects requests that set both GoogleSearchRetrieval and
response_schema. The orchestrator already provides web content via
SearxNG + scraping, so grounding is unnecessary here.

backend/internal/domain/market/research/orchestrator.go

@@ -118,7 +118,6 @@ func callLLM(ctx context.Context, p ai.Provider, userPrompt string, schema []byt
 		SystemPrompt: SystemPrompt,
 		UserMessage:  userPrompt,
 		JSONSchema:   schema,
-		Grounded:     true,
 		CallType:     "research",
 	})
 }