* fix: update PLUGIN.md and CONTRIBUTING.md for single-plugin architecture
After #50 merged auth0-sdks into auth0, PLUGIN.md and CONTRIBUTING.md
still documented the old two-plugin architecture.
PLUGIN.md: Complete rewrite reflecting single unified plugin
CONTRIBUTING.md: Update all paths from plugins/auth0-sdks/ to plugins/auth0/
* fix: add missing README.md to tree, normalize keywords across configs
- PLUGIN.md: add plugins/auth0/README.md to directory tree
- Normalize keyword lists across Claude/Cursor marketplace.json and
Cursor plugin.json to identical 27-keyword set
- Add missing keywords: flask, springboot, java, spa-js
- Remove stale keywords: servlet, java-mvc, express-jwt, fastify-api