feat: implement flash messages system with auto-dismiss notifications

- Add flash message helper and styles for consistent notifications
- Replace Devise error messages with flash-based notifications
- Add dashboard page with event statistics
- Configure SMTP settings for development and production
- Update authentication controllers to use flash messages
- Add JavaScript controller for auto-dismiss functionality

app/assets/stylesheets/application.postcss.css

@@ -3,6 +3,9 @@
 /* Import Tailwind using PostCSS */
 @import "tailwindcss";
 
+/* Import flash message styles */
+@import "components/flash";
+
 /** Default text color */
 body {
     color: #555555;