feat: author pages with /authors/:id route (0.16.0)

- `GET /v1/authors/:id` returns `AuthorWithCount` (id, name, manga_count).
- `GET /v1/authors/:id/mangas` paged works by that author.
- `GET /v1/authors?search=` autocomplete (already used by Phase 1 forms;
  now formally exposed).
- New `/authors/:id` page on the frontend; author chips on the manga
  detail page (added in Phase 1) now link to a real page.
- Extracts `lib/components/MangaCard.svelte` — already used by the home
  page, ready for the collection page in Phase 3.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/routes/authors/[id]/+page.svelte

@@ -0,0 +1,96 @@
+<script lang="ts">
+    import MangaCard from '$lib/components/MangaCard.svelte';
+    import ArrowLeft from '@lucide/svelte/icons/arrow-left';
+
+    let { data } = $props();
+    const author = $derived(data.author);
+    const mangas = $derived(data.mangas);
+    const total = $derived(data.total);
+</script>
+
+<svelte:head>
+    <title>{author.name} — Mangalord</title>
+</svelte:head>
+
+<nav class="back">
+    <a href="/" class="back-link">
+        <ArrowLeft size={16} aria-hidden="true" />
+        <span>Back to search</span>
+    </a>
+</nav>
+
+<header class="overview">
+    <h1 data-testid="author-name">{author.name}</h1>
+    <p class="count" data-testid="author-manga-count">
+        {author.manga_count}
+        {author.manga_count === 1 ? 'work' : 'works'}
+    </p>
+</header>
+
+{#if mangas.length === 0}
+    <p class="status" data-testid="author-no-mangas">
+        No mangas attributed to this author.
+    </p>
+{:else}
+    {#if total != null}
+        <p class="meta" data-testid="author-shown-of-total">
+            Showing {mangas.length} of {total}
+        </p>
+    {/if}
+    <ul class="manga-grid" data-testid="author-manga-list">
+        {#each mangas as m (m.id)}
+            <MangaCard manga={m} testid={`author-manga-${m.id}`} />
+        {/each}
+    </ul>
+{/if}
+
+<style>
+    .back {
+        margin-bottom: var(--space-3);
+    }
+
+    .back-link {
+        display: inline-flex;
+        align-items: center;
+        gap: var(--space-1);
+        color: var(--text-muted);
+        font-size: var(--font-sm);
+    }
+
+    .back-link:hover {
+        color: var(--primary);
+        text-decoration: none;
+    }
+
+    .overview {
+        margin-bottom: var(--space-5);
+    }
+
+    .overview h1 {
+        margin: 0 0 var(--space-1);
+    }
+
+    .count {
+        color: var(--text-muted);
+        margin: 0 0 var(--space-2);
+    }
+
+    .meta {
+        color: var(--text-muted);
+        font-size: var(--font-sm);
+        margin: 0 0 var(--space-3);
+    }
+
+    .status {
+        color: var(--text-muted);
+    }
+
+    .manga-grid {
+        list-style: none;
+        padding: 0;
+        margin: 0;
+        display: grid;
+        grid-template-columns: repeat(auto-fill, minmax(140px, 1fr));
+        gap: var(--space-4);
+    }
+</style>