Separate structured logs from human-readable output

Move SetupLogger() to a standalone function called before config.Load()
so the logger is available from the very start. Replace all fmt.Printf
calls in config.go with slog calls. Redirect banner and endpoint info
to stderr, keeping stdout clean for structured log output (JSON/text).

Fixes #5

internal/config/config.go

@@ -69,8 +69,10 @@ type yamlConfig struct {
 	} `yaml:"api"`
 }
 
-// Load returns configuration with defaults
-func Load() *Config {
+// Load returns configuration with defaults. The provided logger is used for
+// all startup messages so that output format stays consistent (JSON or text)
+// with the rest of the application logs.
+func Load(log *slog.Logger) *Config {
 	dataPath := getEnv("STRIX_DATA_PATH", "./data")
 
 	cfg := &Config{
@@ -127,14 +129,19 @@ func Load() *Config {
 
 	// Validate listen address
 	if err := validateListen(cfg.Server.Listen); err != nil {
-		fmt.Fprintf(os.Stderr, "ERROR: Invalid listen address '%s': %v\n", cfg.Server.Listen, err)
-		fmt.Fprintf(os.Stderr, "Using default: :4567\n")
+		log.Error("invalid listen address, using default :4567",
+			slog.String("address", cfg.Server.Listen),
+			slog.String("error", err.Error()),
+		)
 		cfg.Server.Listen = ":4567"
 		configSource = "default (validation failed)"
 	}
 
 	// Log configuration source
-	fmt.Printf("INFO: API listen address '%s' loaded from %s\n", cfg.Server.Listen, configSource)
+	log.Info("configuration loaded",
+		slog.String("listen", cfg.Server.Listen),
+		slog.String("source", configSource),
+	)
 
 	return cfg
 }
@@ -226,12 +233,30 @@ func validateListen(listen string) error {
 	return nil
 }
 
-// SetupLogger configures the global logger. It returns the logger and a
-// SecretStore that can be used to register credentials for automatic masking
-// in all log output.
-func (c *Config) SetupLogger() (*slog.Logger, *logger.SecretStore) {
+// SetupLogger creates the application logger by reading log configuration
+// from environment variables and Home Assistant options. It must be called
+// before Load() so that all startup messages use a consistent output format.
+//
+// Configuration priority: defaults < HA options < environment variables.
+func SetupLogger() (*slog.Logger, *logger.SecretStore) {
+	// Read log settings from environment (same defaults as Config)
+	logLevel := getEnv("STRIX_LOG_LEVEL", "info")
+	logFormat := getEnv("STRIX_LOG_FORMAT", "json")
+
+	// Apply Home Assistant overrides if running as HA add-on
+	if data, err := os.ReadFile("/data/options.json"); err == nil {
+		var opts haOptions
+		if err := json.Unmarshal(data, &opts); err == nil {
+			if opts.LogLevel != "" {
+				logLevel = opts.LogLevel
+			}
+			// Home Assistant add-on always uses JSON logging for the HA log viewer
+			logFormat = "json"
+		}
+	}
+
 	var level slog.Level
-	switch c.Logger.Level {
+	switch logLevel {
 	case "debug":
 		level = slog.LevelDebug
 	case "warn":
@@ -242,15 +267,15 @@ func (c *Config) SetupLogger() (*slog.Logger, *logger.SecretStore) {
 		level = slog.LevelInfo
 	}
 
-	opts := &slog.HandlerOptions{
+	handlerOpts := &slog.HandlerOptions{
 		Level: level,
 	}
 
 	var handler slog.Handler
-	if c.Logger.Format == "json" {
-		handler = slog.NewJSONHandler(os.Stdout, opts)
+	if logFormat == "json" {
+		handler = slog.NewJSONHandler(os.Stdout, handlerOpts)
 	} else {
-		handler = slog.NewTextHandler(os.Stdout, opts)
+		handler = slog.NewTextHandler(os.Stdout, handlerOpts)
 	}
 
 	secrets := logger.NewSecretStore()