feat(config): add logging configuration fields

config.example.yaml

@@ -45,3 +45,11 @@ sanitize:
       replace: "claude.ai"
     - match: "opencode"
       replace: "agent"
+
+logging:
+  level: info
+  # file: /var/log/anthropic-proxy.log  # omit to log to stderr
+  # max_size_mb: 100
+  # max_backups: 5
+  # max_age_days: 30
+  # compress: true

internal/config/config.go

@@ -15,6 +15,7 @@ type Config struct {
 	APIKeys      []string       `yaml:"api_keys"`
 	ClaudeBinary string         `yaml:"claude_binary"`
 	Sanitize     SanitizeConfig `yaml:"sanitize"`
+	Logging      LoggingConfig  `yaml:"logging"`
 }
 
 type SanitizeConfig struct {
@@ -33,6 +34,15 @@ type ReplaceRule struct {
 	Replace string `yaml:"replace"`
 }
 
+type LoggingConfig struct {
+	Level      string `yaml:"level"`
+	File       string `yaml:"file"`
+	MaxSizeMB  int    `yaml:"max_size_mb"`
+	MaxBackups int    `yaml:"max_backups"`
+	MaxAgeDays int    `yaml:"max_age_days"`
+	Compress   bool   `yaml:"compress"`
+}
+
 type claudeCredentialsJSON struct {
 	ClaudeAiOauth struct {
 		AccessToken      string `json:"accessToken"`
@@ -53,6 +63,19 @@ func Load(path string) (*Config, error) {
 		return nil, fmt.Errorf("parse config: %w", err)
 	}
 
+	if cfg.Logging.Level == "" {
+		cfg.Logging.Level = "info"
+	}
+	if cfg.Logging.MaxSizeMB == 0 {
+		cfg.Logging.MaxSizeMB = 100
+	}
+	if cfg.Logging.MaxBackups == 0 {
+		cfg.Logging.MaxBackups = 5
+	}
+	if cfg.Logging.MaxAgeDays == 0 {
+		cfg.Logging.MaxAgeDays = 30
+	}
+
 	// Check for deprecated claude_credentials field
 	var rawCfg map[string]interface{}
 	if err := yaml.Unmarshal(data, &rawCfg); err == nil {