log(envutil): add debug logging to env var parse fallbacks

Add a debug logger to internal/envutil/envutil.go to surface
misconfiguration earlier. The logger emits a debug message whenever
an environment variable is set but cannot be used (invalid integer,
unparseable duration, unrecognized boolean value), helping operators
quickly identify why a configured value is being silently ignored.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: github-actions[bot]

internal/envutil/envutil.go

@@ -5,8 +5,12 @@ import (
 	"strconv"
 	"strings"
 	"time"
+
+	"github.com/github/gh-aw-mcpg/internal/logger"
 )
 
+var logEnvUtil = logger.New("envutil:envutil")
+
 // GetEnvString returns the value of the environment variable specified by envKey.
 // If the environment variable is not set or is empty, it returns the defaultValue.
 func GetEnvString(envKey, defaultValue string) string {
@@ -25,6 +29,7 @@ func GetEnvInt(envKey string, defaultValue int) int {
 		if value, err := strconv.Atoi(envValue); err == nil && value > 0 {
 			return value
 		}
+		logEnvUtil.Printf("GetEnvInt: %s=%q is not a valid positive integer, using default=%d", envKey, envValue, defaultValue)
 	}
 	return defaultValue
 }
@@ -37,6 +42,7 @@ func GetEnvDuration(envKey string, defaultValue time.Duration) time.Duration {
 		if d, err := time.ParseDuration(envValue); err == nil && d > 0 {
 			return d
 		}
+		logEnvUtil.Printf("GetEnvDuration: %s=%q is not a valid positive duration, using default=%v", envKey, envValue, defaultValue)
 	}
 	return defaultValue
 }
@@ -54,6 +60,7 @@ func GetEnvBool(envKey string, defaultValue bool) bool {
 		case "0", "false", "no", "off":
 			return false
 		}
+		logEnvUtil.Printf("GetEnvBool: %s=%q is not a recognized boolean value, using default=%v", envKey, envValue, defaultValue)
 	}
 	return defaultValue
 }