feat: add config loading with YAML, env override, and hot-reload

internal/config/config.go

@@ -0,0 +1,53 @@
+package config
+
+import (
+	"sync/atomic"
+)
+
+// DoubaoConfig holds 火山引擎豆包 ASR credentials.
+type DoubaoConfig struct {
+	AppKey     string `yaml:"app_key"`
+	AccessKey  string `yaml:"access_key"`
+	ResourceID string `yaml:"resource_id"`
+}
+
+// ServerConfig holds server settings.
+type ServerConfig struct {
+	Port    int  `yaml:"port"`
+	TLSAuto bool `yaml:"tls_auto"`
+}
+
+// Config is the top-level configuration.
+type Config struct {
+	Doubao DoubaoConfig `yaml:"doubao"`
+	Server ServerConfig `yaml:"server"`
+}
+
+// defaults returns a Config with default values.
+func defaults() Config {
+	return Config{
+		Doubao: DoubaoConfig{
+			ResourceID: "volc.seedasr.sauc.duration",
+		},
+		Server: ServerConfig{
+			Port:    8443,
+			TLSAuto: true,
+		},
+	}
+}
+
+// global holds the current config atomically for concurrent reads.
+var global atomic.Value
+
+// Get returns the current config snapshot. Safe for concurrent use.
+func Get() Config {
+	if v := global.Load(); v != nil {
+		return v.(Config)
+	}
+	return defaults()
+}
+
+// store updates the global config.
+func store(cfg Config) {
+	global.Store(cfg)
+}