split-pdf skill: replace deprecated PyPDF2 with pypdf

[powyncify]

The tool is clever, and the author deserves kudos for open-sourcing it. Here's a suggestion: In .claude/skills/split-pdf/SKILL.md, the splitting script uses PyPDF2.

from PyPDF2 import PdfReader, PdfWriter

And the fallback install is:

pip install PyPDF2

PyPDF2 has been officially deprecated and superseded by (the confusingly named) pypdf (same maintainer, drop-in replacement). The fix is two find-and-replace changes — the API is identical:

from pypdf import PdfReader, PdfWriter

pip install pypdf

No other changes needed.