fix: Update Gemini safety settings to use 'OFF' as default

setting/model_setting/gemini.go

@@ -6,7 +6,7 @@ import (
 )
 
 var geminiSafetySettings = map[string]string{
-	"default":                       "BLOCK_NONE",
+	"default":                       "OFF",
 	"HARM_CATEGORY_CIVIC_INTEGRITY": "BLOCK_NONE",
 }