feat: Complete plugin lifecycle management with lazy loading and runtime reload

Major changes:
- Add unload() method to all plugins for proper cleanup (unregister commands/providers/LSP clients, destroy widgets, clear state)
- Implement lazy widget loading via "show" signal across all containers
- Add autoload: false manifest option for manual/conditional plugin loading
- Add Plugins UI with runtime load/unload toggle via Ctrl+Shift+p
- Implement controller unregistration system with proper signal disconnection
- Add new events: UnregisterCommandEvent, GetFilesEvent, GetSourceViewsEvent, TogglePluginsUiEvent
- Fix signal leaks by tracking and disconnecting handlers in widgets (search/replace, LSP manager, tabs, telescope, markdown preview)
- Add Save/Save As to tabs context menu
- Improve search/replace behavior (selection handling, focus management)
- Add telescope file initialization from existing loaded files
- Refactor plugin reload watcher to dynamically add/remove plugins on filesystem changes
- Add new plugins: file_history, extend_source_view_menu, godot_lsp_client
- Fix bug in prettify_json (undefined variable reference

plugins/ui/template/plugin.py

@@ -24,8 +24,16 @@ class Plugin(PluginUI):
         ui_element = self.request_ui_element("header-container")
         ui_element.add( self.generate_plugin_element() )
 
+    def unload(self):
+        ui_element  = self.request_ui_element("header-container")
+        self.button = self.generate_plugin_element()
+
+        ui_element.add( self.button )
+
     def run(self):
-        ...
+        self.button.disconnect_by_func(self.send_message)
+        self.button.destroy()
+        del button
  
     def generate_plugin_element(self):
         button = Gtk.Button(label = "Hello, World!")