feat(api): add structured JSON access log with request-id correlation

backend/internal/config/config_test.go

@@ -108,6 +108,32 @@ func TestLoad_GarminTokenStoreRootExplicitOverridesDefault(t *testing.T) {
 	}
 }
 
+func TestLoad_LogLevelDefaultsToInfo(t *testing.T) {
+	setRequiredEnv(t)
+	t.Setenv("GENIUSRUN_LOG_LEVEL", "")
+
+	cfg, err := Load()
+	if err != nil {
+		t.Fatalf("Load: %v", err)
+	}
+	if cfg.LogLevel != "info" {
+		t.Errorf("LogLevel = %q, want default %q", cfg.LogLevel, "info")
+	}
+}
+
+func TestLoad_LogLevelExplicitOverridesDefault(t *testing.T) {
+	setRequiredEnv(t)
+	t.Setenv("GENIUSRUN_LOG_LEVEL", "debug")
+
+	cfg, err := Load()
+	if err != nil {
+		t.Fatalf("Load: %v", err)
+	}
+	if cfg.LogLevel != "debug" {
+		t.Errorf("LogLevel = %q, want debug", cfg.LogLevel)
+	}
+}
+
 func TestLoad_GarminPythonPathDefaultsToPython3(t *testing.T) {
 	setRequiredEnv(t)
 	t.Setenv("GARMIN_WRAPPER_PYTHON", "")