feat: implement user authentication and license management system

- Added schema for users, licenses, and license hostnames in the database.
- Created storage utility for reading and writing JSON files.
- Developed user service for user registration, authentication, and retrieval.
- Implemented authentication middleware to protect routes.
- Built LicenseCard component to display license details.
- Created SiteNav component for navigation with user authentication status.
- Established AuthContext for managing authentication state and actions.
- Developed Home page to display available plugins.
- Created LicenseManager page for managing licenses with forms for creation and verification.
- Implemented PluginDetail page to show detailed information about a specific plugin.
- Added utility functions for date formatting.

.env.example

@@ -0,0 +1,10 @@
+# MariaDB / MySQL connection
+DB_HOST=127.0.0.1
+DB_PORT=3306
+DB_USER=root
+DB_PASSWORD=secret
+DB_NAME=siti_plugin_repo
+
+# Authentication
+JWT_SECRET=please-change-me
+JWT_EXPIRES_IN=7d