feat: add teaching asset prompts

internal/config/config.go

@@ -6,6 +6,7 @@ const (
 	defaultHTTPAddr        = ":8080"
 	defaultEnvironment     = "development"
 	defaultModelKey        = "deepseek-v4-flash"
+	defaultImageModelKey   = "gpt-image-v2"
 	defaultThirdOneBin     = "thirdone"
 	defaultWorkflowRuntime = ""
 )
@@ -15,6 +16,7 @@ type Config struct {
 	Environment     string
 	WorkflowRuntime string
 	ModelKey        string
+	ImageModelKey   string
 	ThirdOneBin     string
 }
 
@@ -24,6 +26,7 @@ func LoadFromEnv() Config {
 		Environment:     envOrDefault("TUTOR_ENV", defaultEnvironment),
 		WorkflowRuntime: envOrDefault("TUTOR_WORKFLOW_RUNTIME", defaultWorkflowRuntime),
 		ModelKey:        envOrDefault("TUTOR_MODEL_KEY", defaultModelKey),
+		ImageModelKey:   envOrDefault("TUTOR_IMAGE_MODEL_KEY", defaultImageModelKey),
 		ThirdOneBin:     envOrDefault("THIRDONE_BIN", defaultThirdOneBin),
 	}
 }