feat(bookstack-api-m6n): implement pagination iterator with iter.Seq2

Add generic listAll helper using Go 1.23+ iter.Seq2 for memory-efficient
pagination. Implement ListAll() on BooksService and PagesService.
Tests cover multi-page iteration, early break, errors, and empty results.

pages.go

@@ -3,6 +3,7 @@ package bookstack
 import (
 	"context"
 	"fmt"
+	"iter"
 )
 
 // PagesService handles operations on pages.
@@ -20,6 +21,11 @@ func (s *PagesService) List(ctx context.Context, opts *ListOptions) ([]Page, err
 	return resp.Data, nil
 }
 
+// ListAll returns an iterator over all pages, handling pagination automatically.
+func (s *PagesService) ListAll(ctx context.Context) iter.Seq2[Page, error] {
+	return listAll[Page](ctx, s.client, "/api/pages")
+}
+
 // Get retrieves a single page by ID, including its content.
 func (s *PagesService) Get(ctx context.Context, id int) (*Page, error) {
 	var page Page