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

backend/internal/config/config.go

@@ -37,6 +37,8 @@ type Config struct {
 
 	MinConfidence        float64
 	IncrementalSyncEvery time.Duration
+	// LogLevel controls internal/applog's JSON logger ("debug"|"info"|"warn"|"error").
+	LogLevel string
 
 	// OIDC login gate (Keycloak). BackendURL is this app's own externally
 	// reachable origin (e.g. "https://geniusrun.example.com") -- it derives
@@ -75,6 +77,7 @@ func Load() (Config, error) {
 		GarminTokenStoreRoot: os.Getenv("GARMIN_TOKENSTORE"),
 		MinConfidence:        getEnvFloat("GENIUSRUN_MIN_CONFIDENCE", 0.6),
 		IncrementalSyncEvery: getEnvDuration("GENIUSRUN_INCREMENTAL_SYNC_EVERY", 6*time.Hour),
+		LogLevel:             getEnvDefault("GENIUSRUN_LOG_LEVEL", "info"),
 		BackendURL:           strings.TrimRight(os.Getenv("GENIUSRUN_BACKEND_URL"), "/"),
 		OIDCIssuerURL:        os.Getenv("GENIUSRUN_OIDC_ISSUER_URL"),
 		OIDCClientID:         os.Getenv("GENIUSRUN_OIDC_CLIENT_ID"),

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", "")