Refactor: Use @simpleworkjs/conf for configuration

- Replace ENV vars with proper config system
- Add conf/ directory with base, development, production, secrets
- Add secrets.example.js template
- Update .gitignore for secrets.js
- Show environment in startup banner

.gitignore

@@ -4,4 +4,5 @@ data/
 .DS_Store
 *.log
 .env
-.env.local
+.env.local
+conf/secrets.js