Remove .pdm-python from tracking and add to .gitignore

These are local PDM environment markers (machine-specific Python
interpreter paths) that should never be committed. The tracked files
pointed at a stale /Code/ChipFlow/Loom/ path from before the rename.

Co-developed-by: Claude Code v2.1.50 (claude-opus-4-6)

Author: robtaylor

.gitignore

@@ -8,6 +8,7 @@
 __pycache__/
 *.pyc
 *.swp
+.pdm-python
 
 # Claude Code session data
 .claude/