feat: add series support for book organization

API:
- Add /libraries/{id}/series endpoint to list series with book counts
- Add series filter to /books endpoint
- Fix SeriesItem to return first_book_id properly (using CTE with ROW_NUMBER)

Indexer:
- Parse series from parent folder name relative to library root
- Store series in database when indexing books

Backoffice:
- Add Books page with grid view, search, and pagination
- Add Series page showing series with cover images
- Add Library books page filtered by series
- Add book detail page
- Add Series column in libraries list with clickable link
- Create BookCard component for reusable book display
- Add CSS styles for books grid, series grid, and book details
- Add proxy API route for book cover images (fixing CORS issues)

Parser:
- Add series field to ParsedMetadata
- Extract series from file path relative to library root

Books without a parent folder are categorized as 'unclassified' series.

apps/api/src/main.rs

@@ -110,6 +110,7 @@ async fn main() -> anyhow::Result<()> {
         .route("/books", get(books::list_books))
         .route("/books/:id", get(books::get_book))
         .route("/books/:id/pages/:n", get(pages::get_page))
+        .route("/libraries/:library_id/series", get(books::list_series))
         .route("/search", get(search::search_books))
         .route_layer(middleware::from_fn_with_state(state.clone(), read_rate_limit))
         .route_layer(middleware::from_fn_with_state(