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.

apitls/apitls.go

@@ -1,3 +1,14 @@
+// Package apitls provides TLS certificate management with automatic renewal support.
+//
+// This package handles TLS certificate provisioning and management for secure
+// inter-service communication within the NTP Pool project infrastructure.
+// It provides both server and client certificate management through the
+// CertificateProvider interface and includes a trusted CA certificate pool
+// for validating certificates.
+//
+// The package integrates with certman for automatic certificate renewal
+// and includes embedded CA certificates for establishing trust relationships
+// between services.
 package apitls
 
 import (
@@ -13,11 +24,32 @@ import (
 //go:embed ca.pem
 var caBytes []byte
 
+// CertificateProvider defines the interface for providing TLS certificates
+// for both server and client connections. Implementations should handle
+// certificate retrieval, caching, and renewal as needed.
+//
+// This interface supports both server-side certificate provisioning
+// (via GetCertificate) and client-side certificate authentication
+// (via GetClientCertificate).
 type CertificateProvider interface {
+	// GetCertificate retrieves a server certificate based on the client hello information.
+	// This method is typically used in tls.Config.GetCertificate for server-side TLS.
 	GetCertificate(hello *tls.ClientHelloInfo) (*tls.Certificate, error)
+
+	// GetClientCertificate retrieves a client certificate for mutual TLS authentication.
+	// This method is used in tls.Config.GetClientCertificate for client-side TLS.
 	GetClientCertificate(certRequestInfo *tls.CertificateRequestInfo) (*tls.Certificate, error)
 }
 
+// CAPool returns a certificate pool containing trusted CA certificates
+// for validating TLS connections within the NTP Pool infrastructure.
+//
+// The CA certificates are embedded in the binary and include the trusted
+// certificate authorities used for inter-service communication.
+// This pool should be used in tls.Config.RootCAs for client connections
+// or tls.Config.ClientCAs for server connections requiring client certificates.
+//
+// Returns an error if the embedded CA certificates cannot be parsed or loaded.
 func CAPool() (*x509.CertPool, error) {
 	capool := x509.NewCertPool()
 	if !capool.AppendCertsFromPEM(caBytes) {