Add comprehensive godoc documentation to all packages

- Add package-level documentation with usage examples and architecture details
- Document all public types, functions, and methods following godoc conventions
- Remove unused logger.Error type and NewError function
- Apply consistent documentation style across all packages

Packages updated:
- apitls: TLS certificate management with automatic renewal
- config: Environment-based configuration system
- config/depenv: Deployment environment handling
- ekko: Enhanced Echo web framework wrapper
- kafka: Kafka client wrapper with TLS support
- logger: Structured logging with OpenTelemetry integration
- tracing: OpenTelemetry distributed tracing setup
- types: Shared data structures for NTP Pool project
- xff/fastlyxff: Fastly CDN IP range management

All tests pass after documentation changes.

config/config.go

@@ -1,5 +1,18 @@
-// Package config provides NTP Pool specific
-// configuration tools.
+// Package config provides environment-based configuration management for NTP Pool services.
+//
+// This package handles configuration loading from environment variables and provides
+// utilities for constructing URLs for web and management interfaces. It supports
+// deployment-specific settings including hostname configuration, TLS settings,
+// and deployment modes.
+//
+// Configuration is loaded automatically from environment variables:
+//   - deployment_mode: The deployment environment (devel, production, etc.)
+//   - manage_hostname: Hostname for management interface
+//   - web_hostname: Comma-separated list of web hostnames (first is primary)
+//   - manage_tls: Enable TLS for management interface (yes, no, true, false)
+//   - web_tls: Enable TLS for web interface (yes, no, true, false)
+//
+// The package includes code generation for accessor methods using the accessory tool.
 package config
 
 import (
@@ -13,6 +26,9 @@ import (
 
 //go:generate go tool github.com/masaushi/accessory -type Config
 
+// Config holds environment-based configuration for NTP Pool services.
+// It manages hostnames, TLS settings, and deployment modes loaded from
+// environment variables. The struct includes code-generated accessor methods.
 type Config struct {
 	deploymentMode string `accessor:"getter"`
 
@@ -26,6 +42,16 @@ type Config struct {
 	valid bool `accessor:"getter"`
 }
 
+// New creates a new Config instance by loading configuration from environment variables.
+// It automatically parses hostnames, TLS settings, and deployment mode from the environment.
+// The configuration is considered valid if at least one web hostname is provided.
+//
+// Environment variables used:
+//   - deployment_mode: Deployment environment identifier
+//   - manage_hostname: Management interface hostname
+//   - web_hostname: Comma-separated web hostnames (first becomes primary)
+//   - manage_tls: Management interface TLS setting
+//   - web_tls: Web interface TLS setting
 func New() *Config {
 	c := Config{}
 	c.deploymentMode = os.Getenv("deployment_mode")
@@ -46,10 +72,26 @@ func New() *Config {
 	return &c
 }
 
+// WebURL constructs a complete URL for the web interface using the primary web hostname.
+// It automatically selects HTTP or HTTPS based on the web_tls configuration setting.
+//
+// Parameters:
+//   - path: URL path component (should start with "/")
+//   - query: Optional URL query parameters (can be nil)
+//
+// Returns a complete URL string suitable for web interface requests.
 func (c *Config) WebURL(path string, query *url.Values) string {
 	return baseURL(c.webHostname, c.webTLS, path, query)
 }
 
+// ManageURL constructs a complete URL for the management interface using the management hostname.
+// It automatically selects HTTP or HTTPS based on the manage_tls configuration setting.
+//
+// Parameters:
+//   - path: URL path component (should start with "/")
+//   - query: Optional URL query parameters (can be nil)
+//
+// Returns a complete URL string suitable for management interface requests.
 func (c *Config) ManageURL(path string, query *url.Values) string {
 	return baseURL(c.manageHostname, c.webTLS, path, query)
 }