feat(home): add a "Recommended for you" shelf

Surface the content-based /me/recommendations feed as a horizontal shelf on
the homepage, below the Continue-reading shelf. Fetched after the catalogue
(same non-blocking pattern), shown only when signed in and the feed is
non-empty; reuses MangaCard in a fixed-width scroller. Component unit test +
e2e (signed-in shows cards, anonymous hides).

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

frontend/src/routes/+page.svelte

@@ -27,8 +27,10 @@
         type ReadProgressSummary
     } from '$lib/api/read_progress';
     import { isCaughtUp } from '$lib/continueReading';
+    import { listMyRecommendations } from '$lib/api/recommendations';
     import Chip from '$lib/components/Chip.svelte';
     import ContinueReadingShelf from '$lib/components/ContinueReadingShelf.svelte';
+    import RecommendationShelf from '$lib/components/RecommendationShelf.svelte';
     import MangaCard from '$lib/components/MangaCard.svelte';
     import Pager from '$lib/components/Pager.svelte';
     import SegmentedControl from '$lib/components/SegmentedControl.svelte';
@@ -44,6 +46,7 @@
 
     let mangas: MangaCardData[] = $state([]);
     let continueEntries = $state<ReadProgressSummary[]>([]);
+    let recommendations = $state<MangaCardData[]>([]);
     let search = $state('');
     let sort = $state<MangaSort>(DEFAULT_SORT);
     let order = $state<SortOrder>(defaultOrderFor(DEFAULT_SORT));
@@ -320,6 +323,13 @@
             // Never let a history hiccup break the catalogue — leave the
             // shelf hidden.
         }
+        try {
+            // Personal "Recommended for you" feed (empty for guests / no
+            // taste signals yet → shelf hidden).
+            recommendations = await listMyRecommendations();
+        } catch {
+            // Non-critical — leave the shelf hidden on failure.
+        }
     });
 
     // Track viewport in a separate $effect so the listener cleans up on
@@ -478,6 +488,10 @@
     <ContinueReadingShelf entries={continueEntries} />
 {/if}
 
+{#if recommendations.length > 0}
+    <RecommendationShelf mangas={recommendations} />
+{/if}
+
 <form
     onsubmit={onSubmit}
     action="javascript:void(0)"