fix: Add content to plugins/__init__.py to properly expose base_plugin

plugins/__init__.py

@@ -0,0 +1,14 @@
+"""
+Plugins package for EU-Utility.
+
+This package contains both built-in and user-installed plugins.
+The base_plugin module provides the BasePlugin class that all plugins must inherit from.
+"""
+
+# Import base_plugin to make it available as plugins.base_plugin
+try:
+    from plugins import base_plugin
+except ImportError:
+    pass
+
+__all__ = ['base_plugin']