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.ts

@@ -0,0 +1,24 @@
+import { error } from '@sveltejs/kit';
+import { ApiError } from '$lib/api/client';
+import { getAuthor, listAuthorMangas } from '$lib/api/authors';
+import type { PageLoad } from './$types';
+
+export const ssr = false;
+
+export const load: PageLoad = async ({ params }) => {
+    try {
+        const [author, mangas] = await Promise.all([
+            getAuthor(params.id),
+            listAuthorMangas(params.id, { limit: 50 })
+        ]);
+        return { author, mangas: mangas.items, total: mangas.page.total };
+    } catch (e) {
+        // 404 surfaces as a real SvelteKit error so the framework shell
+        // renders the standard not-found page instead of the route's
+        // happy-path markup with undefined data.
+        if (e instanceof ApiError && e.status === 404) {
+            error(404, 'Author not found');
+        }
+        throw e;
+    }
+};