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/lib/api/authors.test.ts

@@ -0,0 +1,91 @@
+import { describe, it, expect, vi, beforeEach, afterEach, type MockInstance } from 'vitest';
+import { listAuthors, getAuthor, listAuthorMangas } from './authors';
+
+function ok(body: unknown, status = 200): Response {
+    return new Response(JSON.stringify(body), {
+        status,
+        headers: { 'content-type': 'application/json' }
+    });
+}
+
+function envelope(status: number, code: string, message: string): Response {
+    return new Response(JSON.stringify({ error: { code, message } }), {
+        status,
+        headers: { 'content-type': 'application/json' }
+    });
+}
+
+describe('authors api client', () => {
+    let fetchSpy: MockInstance<typeof globalThis.fetch>;
+
+    beforeEach(() => {
+        fetchSpy = vi.spyOn(globalThis, 'fetch');
+    });
+    afterEach(() => {
+        vi.restoreAllMocks();
+    });
+
+    it('listAuthors GETs /v1/authors with no params by default', async () => {
+        fetchSpy.mockResolvedValueOnce(ok([]));
+        await listAuthors();
+        const url = fetchSpy.mock.calls[0][0] as string;
+        expect(url).toMatch(/\/v1\/authors$/);
+    });
+
+    it('listAuthors encodes search, limit, offset', async () => {
+        fetchSpy.mockResolvedValueOnce(ok([]));
+        await listAuthors({ search: 'miura', limit: 5, offset: 0 });
+        const url = fetchSpy.mock.calls[0][0] as string;
+        expect(url).toContain('search=miura');
+        expect(url).toContain('limit=5');
+        expect(url).toContain('offset=0');
+    });
+
+    it('getAuthor returns the AuthorWithCount shape', async () => {
+        fetchSpy.mockResolvedValueOnce(
+            ok({
+                id: 'a1',
+                name: 'Kentaro Miura',
+                created_at: '2026-01-01T00:00:00Z',
+                manga_count: 3
+            })
+        );
+        const a = await getAuthor('a1');
+        expect(a.name).toBe('Kentaro Miura');
+        expect(a.manga_count).toBe(3);
+    });
+
+    it('getAuthor surfaces 404 as ApiError', async () => {
+        fetchSpy.mockResolvedValueOnce(envelope(404, 'not_found', 'not found'));
+        await expect(getAuthor('missing')).rejects.toMatchObject({
+            status: 404,
+            code: 'not_found'
+        });
+    });
+
+    it('listAuthorMangas hits the nested route and forwards pagination', async () => {
+        fetchSpy.mockResolvedValueOnce(
+            ok({
+                items: [
+                    {
+                        id: 'm1',
+                        title: 'Berserk',
+                        status: 'ongoing',
+                        alt_titles: [],
+                        description: null,
+                        cover_image_path: null,
+                        created_at: '2026-01-01T00:00:00Z',
+                        updated_at: '2026-01-01T00:00:00Z'
+                    }
+                ],
+                page: { limit: 50, offset: 0, total: 1 }
+            })
+        );
+        const result = await listAuthorMangas('a1', { limit: 20, offset: 10 });
+        expect(result.items[0].title).toBe('Berserk');
+        const url = fetchSpy.mock.calls[0][0] as string;
+        expect(url).toMatch(/\/v1\/authors\/a1\/mangas\?/);
+        expect(url).toContain('limit=20');
+        expect(url).toContain('offset=10');
+    });
+});