fix: use local prettier from package.json and clean up prettierignore

- Replace mirrors-prettier alpha (v4.0.0-alpha.8) with local hook using
  the stable prettier installed via package.json
- Remove .prettierignore entries already handled by the hook's exclude pattern

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.prettierignore

@@ -1,9 +1,4 @@
-dist/
-node_modules/
 coverage.xml
 htmlcov/
 data/
 *.kicad_*
-python/
-package-lock.json
-.venv/