refactor: Extract shared JavaScript utilities (Step 1 of 6)

Create reusable utility modules to eliminate duplication across main.js,
cv-matcher.js, and legal.js:

- js/utils/form-helpers.js: showFieldError, clearFieldErrors, isValidEmail,
  extractApiError — shared form validation and error handling
- js/utils/i18n.js: currentLang, t, applyLanguage, updateLegalLinks,
  browserLang — shared translation and language switching
- js/utils/api.js: checkApiLive, getRecaptchaWebKey, getGoogleTagManagerId,
  loadGoogleTagManager — shared API configuration loading
- js/modules/cookie-consent.js: getConsent, setConsent, initConsent,
  setupConsentHandlers — cookie banner and consent management

All utilities exposed on window.MyAi namespace for use by existing pages.
Full JSDoc headers and inline comments for maintainability.

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

web/wwwroot/js/modules/cookie-consent.js

@@ -0,0 +1,131 @@
+/**
+ * Cookie Consent Management
+ *
+ * Handles cookie banner display, user consent preferences, and localStorage persistence.
+ * Integrates with analytics loading via applyConsent() callback.
+ */
+
+var CONSENT_KEY = "myai_cookie_consent";
+
+/**
+ * Parse consent object from localStorage.
+ * Expected format: { necessary: true, analytics: bool, ts: iso-timestamp }
+ *
+ * @returns {object|null} - Parsed consent object or null if not found or invalid JSON
+ */
+function getConsent() {
+	try {
+		return JSON.parse(localStorage.getItem(CONSENT_KEY));
+	} catch (e) {
+		return null;
+	}
+}
+
+/**
+ * Persist consent object to localStorage as JSON.
+ * Stores { necessary, analytics, ts } properties.
+ *
+ * @param {object} consent - Consent object with necessary, analytics, ts properties
+ */
+function setConsent(consent) {
+	localStorage.setItem(CONSENT_KEY, JSON.stringify(consent));
+}
+
+/**
+ * Apply stored consent preferences.
+ * Currently loads Google Tag Manager if analytics consent is true.
+ * Hook for extending to other tracking/analytics systems.
+ *
+ * @param {object} consent - Consent object from localStorage
+ */
+function applyConsent(consent) {
+	if (window.MyAi && window.MyAi.applyConsent) {
+		window.MyAi.applyConsent(consent);
+	}
+}
+
+/**
+ * Show cookie consent banner with fade-in animation.
+ */
+function showBanner() {
+	$('#cookieBanner').fadeIn(200);
+}
+
+/**
+ * Hide cookie consent banner with fade-out animation.
+ */
+function hideBanner() {
+	$('#cookieBanner').fadeOut(200);
+}
+
+/**
+ * Show "manage cookies" button.
+ * Appears after user has made a consent choice.
+ */
+function showManage() {
+	$('#cookieManage').show();
+}
+
+/**
+ * Initialize cookie consent flow on page load.
+ * If user has already made a choice, apply preferences and show manage button.
+ * If no choice yet, show consent banner.
+ */
+function initConsent() {
+	var consent = getConsent();
+	if (!consent) {
+		showBanner();
+	} else {
+		applyConsent(consent);
+		showManage();
+	}
+}
+
+/**
+ * Bind cookie consent button handlers.
+ * Reject or Necessary-only button → analytics: false
+ * Accept button → analytics: true (and load GTM)
+ * Manage button → show banner again
+ */
+function setupConsentHandlers() {
+	$('#cookieReject, #cookieNecessary').on('click', function () {
+		setConsent({
+			necessary: true,
+			analytics: false,
+			ts: new Date().toISOString()
+		});
+		hideBanner();
+		showManage();
+	});
+
+	$('#cookieAccept').on('click', function () {
+		var consent = {
+			necessary: true,
+			analytics: true,
+			ts: new Date().toISOString()
+		};
+		setConsent(consent);
+		applyConsent(consent);
+		hideBanner();
+		showManage();
+	});
+
+	$('#cookieManage').on('click', function (e) {
+		e.preventDefault();
+		showBanner();
+	});
+}
+
+// Expose consent utilities on window.MyAi
+window.MyAi = window.MyAi || {};
+window.MyAi.getConsent = getConsent;
+window.MyAi.setConsent = setConsent;
+window.MyAi.initConsent = initConsent;
+window.MyAi.showBanner = showBanner;
+window.MyAi.hideBanner = hideBanner;
+
+// Initialize on DOM ready
+$(function() {
+	setupConsentHandlers();
+	initConsent();
+});