refactor: adopt POSITIONS constants, fix ESLint warnings, break menuUtils into modules

- Replace hardcoded position strings with POSITIONS.* constants
- Prefix unused variables with _ to resolve no-unused-vars warnings
- Fix no-prototype-builtins with Object.prototype.hasOwnProperty.call()
- Extract menuUtils.js (543 lines) into 6 focused modules under menu/
- menuUtils.js now 35 lines, delegates via prototype mixin pattern
- Add 158 unit tests for ConfigManager, MeasurementContainer, ValidationUtils

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/helper/configUtils.js

@@ -76,7 +76,7 @@ class ConfigUtils {
     // loop through objects and merge them obj1 will be updated with obj2 values
     mergeObjects(obj1, obj2) {
         for (let key in obj2) {
-            if (obj2.hasOwnProperty(key)) {
+            if (Object.prototype.hasOwnProperty.call(obj2, key)) {
                 if (typeof obj2[key] === 'object') {
                     if (!obj1[key]) {
                         obj1[key] = {};