feat(bookstack-api-9xo): implement BooksService List and Get

Add listResponse generic type and ListOptions.queryString() helper.
Implement BooksService.List with pagination support and Get with
proper error handling. Include mock server tests.

books.go

@@ -1,6 +1,9 @@
 package bookstack
 
-import "context"
+import (
+	"context"
+	"fmt"
+)
 
 // BooksService handles operations on books.
 type BooksService struct {
@@ -8,36 +11,21 @@ type BooksService struct {
 }
 
 // List returns a list of books with optional filtering.
-// TODO: Implement API call to GET /api/books
 func (s *BooksService) List(ctx context.Context, opts *ListOptions) ([]Book, error) {
-	// Placeholder for future implementation
-	return nil, nil
+	var resp listResponse[Book]
+	err := s.client.do(ctx, "GET", "/api/books"+opts.queryString(), nil, &resp)
+	if err != nil {
+		return nil, err
+	}
+	return resp.Data, nil
 }
 
 // Get retrieves a single book by ID.
-// TODO: Implement API call to GET /api/books/{id}
 func (s *BooksService) Get(ctx context.Context, id int) (*Book, error) {
-	// Placeholder for future implementation
-	return nil, nil
-}
-
-// Create creates a new book.
-// TODO: Implement API call to POST /api/books
-func (s *BooksService) Create(ctx context.Context, book *Book) (*Book, error) {
-	// Placeholder for future implementation
-	return nil, nil
-}
-
-// Update updates an existing book.
-// TODO: Implement API call to PUT /api/books/{id}
-func (s *BooksService) Update(ctx context.Context, id int, book *Book) (*Book, error) {
-	// Placeholder for future implementation
-	return nil, nil
-}
-
-// Delete deletes a book by ID.
-// TODO: Implement API call to DELETE /api/books/{id}
-func (s *BooksService) Delete(ctx context.Context, id int) error {
-	// Placeholder for future implementation
-	return nil
+	var book Book
+	err := s.client.do(ctx, "GET", fmt.Sprintf("/api/books/%d", id), nil, &book)
+	if err != nil {
+		return nil, err
+	}
+	return &book, nil
 }