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.
