feat(pdf): add script to fill PDF forms with annotations

* Implemented `fill_pdf_form_with_annotations.py` to fill PDF forms using text annotations defined in a JSON file.
* Added coordinate transformation from image to PDF dimensions.
* Included error handling for empty fields and annotation properties.

chore(xlsx): add LICENSE and SKILL documentation

* Created LICENSE.txt for xlsx skill with usage terms and restrictions.
* Added SKILL.md for xlsx skill detailing requirements, best practices, and workflows for Excel file creation, editing, and analysis.

feat(xlsx): add script for recalculating Excel formulas

* Introduced `recalc.py` to recalculate Excel formulas using LibreOffice.
* Implemented error checking for common Excel formula errors.
* Provided detailed JSON output for error reporting.

docs(prompt-engineering): add comprehensive prompt engineering guidelines

* Created SKILL.md for prompt-engineering with techniques to optimize LLM interactions.
* Included sections on few-shot learning, chain-of-thought prompting, and error recovery.
* Documented principles of persuasion for effective prompt design.