feat: add useAuth composable with user tier detection

resources/js/composables/useAuth.js

@@ -0,0 +1,44 @@
+import { ref, computed } from 'vue'
+import api from '../axios.js'
+
+const user = ref(null)
+const loading = ref(false)
+const fetched = ref(false)
+
+export function useAuth() {
+    const isAuthenticated = computed(() => user.value !== null)
+
+    const userTier = computed(() => {
+        if (!user.value) {
+            return 'guest'
+        }
+        return user.value.tier ?? 'free'
+    })
+
+    const isPaidTier = computed(() => {
+        return ['basic', 'plus', 'pro'].includes(userTier.value)
+    })
+
+    async function fetchUser() {
+        if (fetched.value) {
+            return
+        }
+        loading.value = true
+        try {
+            const response = await api.get('/auth/me')
+            user.value = response.data
+        } catch {
+            user.value = null
+        } finally {
+            loading.value = false
+            fetched.value = true
+        }
+    }
+
+    function clearUser() {
+        user.value = null
+        fetched.value = false
+    }
+
+    return { user, loading, isAuthenticated, userTier, isPaidTier, fetchUser, clearUser }
+}