Rename pathview_server to pathview and add convert API

[milanofthe]

Summary

• Rename pathview_server/ → pathview/ so the importable module matches the pip package name
• Add pathview.converter module with a public convert() API extracted from scripts/pvm2py.py
• from pathview import convert now works — loads bundled registry, returns Python script string
• scripts/pvm2py.py now imports from pathview.converter instead of duplicating logic
• scripts/extract.py writes registry to both scripts/generated/ and pathview/data/