feat: SSR shopping list by fetching initial data server-side

Server load now fetches the shopping list from the DB and passes it as
initialList. The sync layer seeds state immediately in the script block
(not onMount) so SSR renders the full list. SSE connects client-side
in onMount for real-time updates.

src/lib/js/shoppingSync.svelte.ts

@@ -166,6 +166,20 @@ export function createShoppingSync() {
     }
   }
 
+  /** Seed state from server-loaded data (safe to call during SSR). */
+  function seed(initialList: { version: number; items: ShoppingItem[] }, token?: string | null) {
+    if (token) shareToken = token;
+    version = initialList.version;
+    items = initialList.items || [];
+    status = 'synced';
+  }
+
+  /** Connect SSE for real-time updates (client-only, call in onMount). */
+  function connect(token?: string | null) {
+    if (token) shareToken = token;
+    connectSSE();
+  }
+
   function addItem(name: string, user: string, category = 'Sonstiges') {
     items = [...items, {
       id: generateId(),
@@ -211,6 +225,8 @@ export function createShoppingSync() {
     get version() { return version; },
     apiUrl,
     init,
+    seed,
+    connect,
     addItem,
     toggleItem,
     removeItem,

src/routes/[cospendRoot=cospendRoot]/list/+page.server.ts

@@ -1,6 +1,8 @@
 import type { PageServerLoad } from './$types';
 import { redirect } from '@sveltejs/kit';
 import { getShoppingUser } from '$lib/server/shoppingAuth';
+import { dbConnect } from '$utils/db';
+import { ShoppingList } from '$models/ShoppingList';
 
 export const load: PageServerLoad = async ({ locals, url }) => {
   const session = await locals.auth();
@@ -9,9 +11,24 @@ export const load: PageServerLoad = async ({ locals, url }) => {
   // Allow access with valid share token even without session
   if (!session && token) {
     const user = await getShoppingUser(locals, url);
-    if (user) return { session: null, shareToken: token };
+    if (user) {
+      await dbConnect();
+      const list = await ShoppingList.findOne().lean();
+      return {
+        session: null,
+        shareToken: token,
+        initialList: list ? { version: list.version, items: list.items } : { version: 0, items: [] }
+      };
+    }
   }
 
   if (!session) throw redirect(302, '/login');
-  return { session, shareToken: null };
+
+  await dbConnect();
+  const list = await ShoppingList.findOne().lean();
+  return {
+    session,
+    shareToken: null,
+    initialList: list ? { version: list.version, items: list.items } : { version: 0, items: [] }
+  };
 };

src/routes/[cospendRoot=cospendRoot]/list/+page.svelte

@@ -20,6 +20,11 @@
   let isGuest = $derived(!data.session);
   const sync = getShoppingSync();
 
+  // Seed sync state immediately so SSR can render the list
+  if (data.initialList) {
+    sync.seed(data.initialList, data.shareToken);
+  }
+
   const lang = $derived(detectCospendLang($page.url.pathname));
   const loc = $derived(locale(lang));
 
@@ -141,7 +146,13 @@
   let checkedCount = $derived(sync.items.filter(i => i.checked).length);
   let totalCount = $derived(sync.items.length);
 
-  onMount(() => { sync.init(shareToken); });
+  onMount(() => {
+    if (data.initialList) {
+      sync.connect(shareToken);
+    } else {
+      sync.init(shareToken);
+    }
+  });
   onDestroy(() => { sync.disconnect(); });
 
   async function addItem() {