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/menu/toggles.js

@@ -0,0 +1,56 @@
+/**
+ * Toggle initialization methods for MenuUtils.
+ * Controls visibility of UI elements based on checkbox/dropdown state.
+ */
+
+const toggles = {
+  initBasicToggles(elements) {
+    // Toggle visibility for log level
+    elements.logCheckbox.addEventListener("change", function () {
+      elements.rowLogLevel.style.display = this.checked ? "block" : "none";
+    });
+    elements.rowLogLevel.style.display = elements.logCheckbox.checked
+      ? "block"
+      : "none";
+  },
+
+  // Define the initialize toggles function within scope
+  initMeasurementToggles(elements) {
+    // Toggle visibility for scaling inputs
+    elements.scalingCheckbox.addEventListener("change", function () {
+      elements.rowInputMin.style.display = this.checked ? "block" : "none";
+      elements.rowInputMax.style.display = this.checked ? "block" : "none";
+    });
+
+    // Set initial states
+    elements.rowInputMin.style.display = elements.scalingCheckbox.checked
+      ? "block"
+      : "none";
+    elements.rowInputMax.style.display = elements.scalingCheckbox.checked
+      ? "block"
+      : "none";
+  },
+
+  initTensionToggles(elements, node) {
+    const currentMethod = node.interpolationMethod;
+    elements.rowTension.style.display =
+      currentMethod === "monotone_cubic_spline" ? "block" : "none";
+    console.log(
+      "Initial tension row display: ",
+      elements.rowTension.style.display
+    );
+
+    elements.interpolationMethodInput.addEventListener("change", function () {
+      const selectedMethod = this.value;
+      console.log(`Interpolation method changed: ${selectedMethod}`);
+      node.interpolationMethod = selectedMethod;
+
+      // Toggle visibility for tension input
+      elements.rowTension.style.display =
+        selectedMethod === "monotone_cubic_spline" ? "block" : "none";
+      console.log("Tension row display: ", elements.rowTension.style.display);
+    });
+  },
+};
+
+module.exports = toggles;