feat: display series metadata (authors, description) from Stripstream API

Fetch metadata from GET /libraries/{id}/series/{name}/metadata and display
authors with icon and description in the series header.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/types/stripstream.ts

@@ -48,6 +48,7 @@ export interface StripstreamSeriesItem {
   book_count: number;
   books_read_count: number;
   first_book_id: string;
+  library_id: string;
 }
 
 export interface StripstreamSeriesPage {
@@ -80,6 +81,15 @@ export interface StripstreamUpdateReadingProgressRequest {
   current_page?: number | null;
 }
 
+export interface StripstreamSeriesMetadata {
+  authors: string[];
+  publishers: string[];
+  description?: string | null;
+  start_year?: number | null;
+  book_author?: string | null;
+  book_language?: string | null;
+}
+
 export interface StripstreamSearchResponse {
   hits: StripstreamSearchHit[];
   series_hits: StripstreamSeriesHit[];