chore: drop accidentally-committed __pycache__/ and gitignore .pyc

The previous commit (5fac9c39) shipped sheets_df.py and inadvertently
included its `__pycache__/sheets_df.cpython-312.pyc` — local Python
import created the bytecode cache during PPE round-trip verification and
`git add skills/lark-sheets/` swept it in.

Remove the pyc and add Python bytecode patterns to .gitignore so the
skill-bundled helper scripts don't pull cache files into future commits.

.gitignore

@@ -7,6 +7,11 @@ bin/
 # Node
 node_modules/
 
+# Python (skill-bundled helper scripts)
+__pycache__/
+*.py[cod]
+*$py.class
+
 
 # OS
 .DS_Store