feat: add AdminMemberTiers page, MemberBadge component, and SettingsLayout; refactor routes and sidebar for improved navigation

src/utils/member-tiers.js

@@ -0,0 +1,23 @@
+// src/utils/member-tiers.js
+import { differenceInDays } from 'date-fns';
+import { DEFAULT_MEMBER_TIERS } from '../config/memberTiers';
+
+export const getTenureDays = (memberSince) => {
+    if (!memberSince) return null;
+    const since = new Date(memberSince);
+    if (Number.isNaN(since.getTime())) return null;
+    return Math.max(0, differenceInDays(new Date(), since));
+};
+
+export const getTierForMember = (memberSince, tiers = DEFAULT_MEMBER_TIERS) => {
+    const days = getTenureDays(memberSince);
+    if (days == null) return tiers[0];
+
+    const match = tiers.find(
+        (tier) =>
+            days >= tier.minDays &&
+            (tier.maxDays == null || days <= tier.maxDays)
+    );
+
+    return match || tiers[0];
+};