feat: loading skeletons on the bookmarks and collections pages

Both loaders now stream the whole result (the single fetch is also the auth
gate) so the page shows a skeleton while it loads instead of the global nav
bar only: a ListRowSkeleton on bookmarks and a MangaGridSkeleton on the
collections grid, resolving to the sign-in / error / empty / list branches.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/src/routes/collections/+page.svelte

@@ -1,26 +1,30 @@
 <script lang="ts">
     import CollectionsGrid from '$lib/components/CollectionsGrid.svelte';
+    import MangaGridSkeleton from '$lib/components/MangaGridSkeleton.svelte';
 
     let { data } = $props();
-    const collections = $derived(data.collections);
 </script>
 
 <h1>Collections</h1>
 
-{#if !data.authenticated}
-    <p class="status">
-        <a href="/login">Sign in</a> to see and manage your collections.
-    </p>
-{:else if data.error}
-    <p class="error" role="alert">{data.error}</p>
-{:else if collections.length === 0}
-    <p class="status" data-testid="collections-empty">
-        You don't have any collections yet. Open any manga and use
-        <strong>Add to collection</strong> to start one.
-    </p>
-{:else}
-    <CollectionsGrid {collections} />
-{/if}
+{#await data.result}
+    <MangaGridSkeleton count={6} />
+{:then r}
+    {#if !r.authenticated}
+        <p class="status">
+            <a href="/login">Sign in</a> to see and manage your collections.
+        </p>
+    {:else if r.error}
+        <p class="error" role="alert">{r.error}</p>
+    {:else if r.collections.length === 0}
+        <p class="status" data-testid="collections-empty">
+            You don't have any collections yet. Open any manga and use
+            <strong>Add to collection</strong> to start one.
+        </p>
+    {:else}
+        <CollectionsGrid collections={r.collections} />
+    {/if}
+{/await}
 
 <style>
     .status {

frontend/src/routes/collections/+page.ts

@@ -5,16 +5,22 @@ import type { PageLoad } from './$types';
 export const ssr = false;
 
 export const load: PageLoad = async () => {
-    try {
-        const page = await listMyCollections({ limit: 200 });
-        return { collections: page.items, authenticated: true, error: null };
-    } catch (e) {
-        if (e instanceof ApiError && e.status === 401) {
-            return { collections: [], authenticated: false, error: null };
-        }
-        if (e instanceof ApiError) {
-            return { collections: [], authenticated: true, error: e.message };
-        }
-        throw e;
-    }
+    // Streamed so the grid shows a skeleton while the single fetch (also the
+    // auth gate) is in flight.
+    return {
+        result: (async () => {
+            try {
+                const page = await listMyCollections({ limit: 200 });
+                return { collections: page.items, authenticated: true, error: null as string | null };
+            } catch (e) {
+                if (e instanceof ApiError && e.status === 401) {
+                    return { collections: [], authenticated: false, error: null as string | null };
+                }
+                if (e instanceof ApiError) {
+                    return { collections: [], authenticated: true, error: e.message };
+                }
+                throw e;
+            }
+        })()
+    };
 };