chore: rename MedAssist to MedAssist-ng in all frontend UI (#74)

Update all visible text from 'MedAssist' to 'MedAssist-ng':
- Auth page titles (login, register)
- Loading/error/initializing states
- SharedSchedule page (loading, expired, error, footer)
- AboutModal fallback text
- i18n strings for export file validation (EN/DE)
- Related test expectations

frontend/src/components/AboutModal.tsx

@@ -80,7 +80,7 @@ export default function AboutModal({ isOpen, onClose }: AboutModalProps) {
 							<path d="M9 2h6M12 2v2" />
 						</svg>
 					</div>
-					<h2>{t("about.appName", "MedAssist")}</h2>
+					<h2>{t("about.appName", "MedAssist-ng")}</h2>
 					<p className="about-tagline">{t("about.description", "Personal medication tracking and reminder app")}</p>
 				</div>
 				<div className="about-versions">

frontend/src/components/Auth.tsx

@@ -339,7 +339,7 @@ export function LoginForm({
 	return (
 		<div className="auth-container">
 			<div className="auth-card">
-				<h1 className="auth-title">💊 MedAssist</h1>
+				<h1 className="auth-title">💊 MedAssist-ng</h1>
 				<h2 className="auth-subtitle">{t("auth.login", "Login")}</h2>
 
 				{/* SSO Login Button */}
@@ -455,7 +455,7 @@ export function RegisterForm({ onSuccess, onSwitchToLogin }: { onSuccess?: () =>
 	return (
 		<div className="auth-container">
 			<div className="auth-card">
-				<h1 className="auth-title">💊 MedAssist</h1>
+				<h1 className="auth-title">💊 MedAssist-ng</h1>
 				<h2 className="auth-subtitle">{t("auth.register", "Create Account")}</h2>
 
 				{/* SSO Login Button - also show on registration */}

frontend/src/components/SharedSchedule.tsx

@@ -455,7 +455,7 @@ export function SharedSchedule() {
 		return (
 			<div className="shared-schedule-page">
 				<div className="shared-schedule-loading">
-					<h1>💊 MedAssist</h1>
+					<h1>💊 MedAssist-ng</h1>
 					<p>{t("common.loading")}</p>
 				</div>
 			</div>
@@ -466,7 +466,7 @@ export function SharedSchedule() {
 		return (
 			<div className="shared-schedule-page">
 				<div className="shared-schedule-error expired">
-					<h1>💊 MedAssist</h1>
+					<h1>💊 MedAssist-ng</h1>
 					<div className="expired-icon">⏰</div>
 					<h2>{t("share.expired.title")}</h2>
 					<p className="expired-message">{t("share.expired.message", { takenBy: expiredData.takenBy })}</p>
@@ -485,7 +485,7 @@ export function SharedSchedule() {
 		return (
 			<div className="shared-schedule-page">
 				<div className="shared-schedule-error">
-					<h1>💊 MedAssist</h1>
+					<h1>💊 MedAssist-ng</h1>
 					<p className="error-message">{error || "Unknown error"}</p>
 				</div>
 			</div>