fix(detail): resync reaction toggle across manga navigation

The detail page component is reused across /manga/A -> /manga/B
navigations (clicking a similar or recommendation card), so
ReactionButtons' locally-held `current` state kept the previous manga's
reaction until interacted with — a visibly wrong thumb on the new page.
Re-seed `current` from the loader-supplied prop via an effect keyed on
mangaId. Also fetch the homepage's two independent /me/* shelves
concurrently (Promise.allSettled) instead of in series.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/lib/components/ReactionButtons.svelte

@@ -18,6 +18,16 @@
     let current = $state<Reaction | null>(initial);
     let busy = $state(false);
 
+    // The detail page reuses this component across manga -> manga navigation
+    // (similar / recommendation cards), so `current` must re-seed when the
+    // loader hands us a new manga's reaction. `mangaId` is referenced so the
+    // effect also re-runs when navigating between two never-reacted mangas
+    // (both `initial === null`).
+    $effect(() => {
+        mangaId;
+        current = initial;
+    });
+
     // Click the active reaction to clear it; click the other to switch.
     async function apply(next: Reaction) {
         if (busy) return;

frontend/src/lib/components/ReactionButtons.svelte.test.ts

@@ -51,6 +51,24 @@ describe('ReactionButtons', () => {
         expect(pressed('reaction-like')).toBe('false');
     });
 
+    it('resyncs when navigated to a different manga', async () => {
+        // The detail page component is reused across /manga/A -> /manga/B
+        // navigations (e.g. clicking a similar or recommendation card), so
+        // new props must overwrite the locally-held reaction state.
+        const { rerender } = render(ReactionButtons, {
+            props: { mangaId: 'm1', initial: 'like' }
+        });
+        expect(pressed('reaction-like')).toBe('true');
+
+        await rerender({ mangaId: 'm2', initial: 'dislike' });
+        expect(pressed('reaction-dislike')).toBe('true');
+        expect(pressed('reaction-like')).toBe('false');
+
+        await rerender({ mangaId: 'm3', initial: null });
+        expect(pressed('reaction-like')).toBe('false');
+        expect(pressed('reaction-dislike')).toBe('false');
+    });
+
     it('rolls back on failure', async () => {
         setReaction.mockRejectedValue(new Error('boom'));
         render(ReactionButtons, { props: { mangaId: 'm1', initial: null } });