fix(web): admin des bibliothèques — UX, gestion d'erreur, styles

- web: AdminPage (admin bibliothèques), client API, styles
- web: nginx

Refs: #15

apps/web/src/api/client.ts

@@ -165,6 +165,9 @@ export const api = {
       fallback: { id: Date.now(), createdAt: new Date().toISOString(), updatedAt: new Date().toISOString(), ...input }
     });
   },
+  async deleteLibrary(id: number): Promise<void> {
+    await request<{ ok: true }>(`/admin/libraries/${id}`, { method: "DELETE" });
+  },
   async scanLibrary(id: number): Promise<JobDto> {
     return request<JobDto>(`/admin/libraries/${id}/scan`, { method: "POST", fallback: mockJobs[0] });
   },