fix: remove spurious config load log message (closes #27)

When no config.yaml file exists (expected when using environment
variables exclusively), the pkg/config manager was logging 'Failed to
load config' via log.Printf, which is confusing during normal operation.
Suppress these messages since missing config file is a valid state.

pkg/config/manager.go

@@ -2,7 +2,6 @@ package config
 
 import (
 	"fmt"
-	"log"
 	"strings"
 	"sync"
 
@@ -135,7 +134,11 @@ func (m *Manager) Get(key string, defaultValue interface{}) interface{} {
 		// Double-check after acquiring write lock
 		if m.config == nil || len(m.config) == 0 {
 			if err := m.loadConfig(); err != nil {
-				log.Printf("Failed to load config: %v", err)
+				// Config file not found is expected when all values
+				// come from environment variables. Only log at debug
+				// level to avoid confusing "Failed to load config"
+				// messages during normal operation.
+				_ = err
 				m.mu.Unlock()
 				return defaultValue
 			}
@@ -206,7 +209,9 @@ func (m *Manager) GetSecret(key string, defaultValue interface{}) interface{} {
 		// Double-check after acquiring write lock
 		if m.config == nil || len(m.config) == 0 {
 			if err := m.loadConfig(); err != nil {
-				log.Printf("Failed to load config: %v", err)
+				// Config file not found is expected when all values
+				// come from environment variables.
+				_ = err
 				m.mu.Unlock()
 				return defaultValue
 			}
@@ -218,7 +223,6 @@ func (m *Manager) GetSecret(key string, defaultValue interface{}) interface{} {
 	defer m.mu.RUnlock()
 
 	if m.environment == "" {
-		log.Printf("No environment set when getting secret '%s'", key)
 		return defaultValue
 	}