Remove pfe dev server config from pfe tools

[bennypowers]

Summary

Remove dev server and related configs from pfe-tools now that @pwrs/cem covers that functionality.

Notes

@pwrs/cem provides: dev server, SSG for demos, etc. - superseding the pfe-tools equivalents.

Checklist

Implementation

• Identify all dev server config in pfe-tools
• Remove superseded dev server config files
• Update any scripts / CI referencing the old config
• Verify npm start still works via cem serve

Reviews

• eslint passes

Ship

• Add changeset
• PR targets staging/pfv6 (NOT main)