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/response_handlers/java.py

@@ -0,0 +1,51 @@
+# Python imports
+
+# Lib imports
+import gi
+gi.require_version('GtkSource', '4')
+
+from gi.repository import GtkSource
+
+# Application imports
+from libs.event_factory import Event_Factory, Code_Event_Types
+
+from .default import DefaultHandler
+
+
+
+class JavaHandler(DefaultHandler):
+    """Java-specific: overrides definition, handles classFileContents."""
+
+    def handle(self, method: str, response, controller):
+        match method:
+            case "textDocument/definition":
+                self._handle_definition(response, controller)
+            case "java/classFileContents":
+                self._handle_class_file_contents(response)
+            case _:
+                super().handle(method, response, controller)
+
+    def _handle_definition(self, response, controller):
+        if not response: return
+
+        uri = response[0]["uri"]
+        if "jdt://" in uri:
+            controller._lsp_java_class_file_contents(uri)
+            return
+
+        self.context._prompt_goto_request(uri, response[0]["range"])
+
+    def _handle_class_file_contents(self, text: str):
+        event = Event_Factory.create_event("get_active_view")
+        self.context.emit_to("source_views", event)
+
+        view = event.response
+        file = view.command.exec("new_file")
+        buffer = view.get_buffer()
+        itr = buffer.get_iter_at_mark(buffer.get_insert())
+        lm = GtkSource.LanguageManager.get_default()
+        language = lm.get_language("java")
+        file.ftype = "java"
+
+        buffer.set_language(language)
+        buffer.insert(itr, text, -1)