Auto Page numbering support

Want to be able to add page numbers to the generated PDF with font configuration. Use case - Printouts.
Once this is done, easy to add a Table of Contents too. #6

I was exploring and found this as one option: https://github.com/vlad-anisov/numbering2pdf/blob/main/numbering2pdf/numbering2pdf.py It uses reportlab to generate empty numbered PDFs and merges those pages with the existing pages one by one.

Happy to work on this issue, if you suggest a preferred method (given your research) to implement this.

Start by reviewing the referenced numbering2pdf.py approach and locating pystitcher's existing PDF generation path. Clarify how page-number placement and font configuration should work, then define tests or sample output that demonstrate numbered pages and the expected print-ready result.

Written by the indexing model from the issue text.