fix: update grok default model to grok-2

Changed grok-beta to grok-2 across backend config, dashboard tests, and frontend monitoring.

internal/config/config.go

@@ -99,7 +99,7 @@ func Load() (*Config, error) {
 
 	v.SetDefault("providers.grok.api_key_env", "GROK_API_KEY")
 	v.SetDefault("providers.grok.base_url", "https://api.x.ai/v1")
-	v.SetDefault("providers.grok.default_model", "grok-beta")
+	v.SetDefault("providers.grok.default_model", "grok-2")
 	v.SetDefault("providers.grok.enabled", true)
 
 	v.SetDefault("providers.ollama.base_url", "http://localhost:11434/v1")

internal/server/dashboard.go

@@ -693,7 +693,7 @@ func (s *Server) handleTestProvider(c *gin.Context) {
 	} else if name == "deepseek" {
 		testReq.Model = "deepseek-chat"
 	} else if name == "grok" {
-		testReq.Model = "grok-beta"
+		testReq.Model = "grok-2"
 	}
 
 	_, err := provider.ChatCompletion(c.Request.Context(), testReq)