Use a pinia store to manage session state

Replace the convoluted useAccountSession composable with a pinia store
that in addition allows for the consolidation of all session related
functions to grouped into one module.

app.vue

@@ -5,4 +5,9 @@
 
 <script setup lang="ts">
 import "~/assets/global.css";
+const event = useRequestEvent();
+const sessionStore = useSessionStore();
+await callOnce("fetch-session", async () => {
+	await sessionStore.fetch(event);
+})
 </script>