Update docx, xlsx, pdf, pptx skills with latest improvements

docx: Add commenting and track-changes support. Reorganize OOXML
tooling into a shared office/ module.

pptx: Streamline SKILL.md, add slide-editing and pptxgenjs guides,
bundle html2pptx as a tgz. Reorganize OOXML tooling into a shared
office/ module.

xlsx: Move recalc script into scripts/ and expand it. Add shared
office/ module for OOXML pack/unpack/validate.

pdf: Improve form-filling workflow with new form-structure extraction
script and updated field-info extraction.

skills/pdf/scripts/convert_pdf_to_images.py

@@ -4,14 +4,12 @@ import sys
 from pdf2image import convert_from_path
 
 
-# Converts each page of a PDF to a PNG image.
 
 
 def convert(pdf_path, output_dir, max_dim=1000):
     images = convert_from_path(pdf_path, dpi=200)
 
     for i, image in enumerate(images):
-        # Scale image if needed to keep width/height under `max_dim`
         width, height = image.size
         if width > max_dim or height > max_dim:
             scale_factor = min(max_dim / width, max_dim / height)