refactor(lsp-manager): replace handler architecture with response registry and modular providers

* Remove legacy handlers system (BaseHandler, DefaultHandler, JavaHandler, PythonHandler, HandlerRegistry)
* Introduce response_handlers module with ResponseRegistry for LSP response routing
* Replace HandlerRegistry usage in LSPManager with ResponseRegistry
* Convert LSPManagerUI client lifecycle to GObject signals
* Remove GLib.idle_add usage in LSP client event dispatch
* Move completion request logic into LSPServerEventsMixin
* Replace provider.py and provider_response_cache.py with modular provider/ package
* Simplify plugin wiring via response_registry.set_event_hub()

This refactor decouples response handling, simplifies event flow, and prepares
the LSP manager for easier language-specific extensions.

plugins/code/ui/lsp_manager/mixins/lsp_server_events_mixin.py

@@ -76,6 +76,18 @@ class LSPServerEventsMixin:
 
         GLib.idle_add( move_cursor, buffer, pointer_pos )
 
+    def _prompt_completion_request(self):
+        event = Event_Factory.create_event("get_active_view")
+        self.emit_to("source_views", event)
+        view  = event.response
+
+        event = Event_Factory.create_event(
+            "request_completion",
+            view     = view,
+            provider = self._provider
+        )
+        self.emit_to("completion", event)
+
     def _handle_java_class_file_contents(self, text: str):
         event  = Event_Factory.create_event(
             "get_active_view",