refactor(lsp): replace LSPManager with controller-based architecture

- Remove legacy LSPManager dialog implementation
- Introduce LSPController as the central LSP entry point
- Route UI interactions through lsp_controller.lsp_manager_ui
- Move client lifecycle handling out of ProviderResponseCache
- Simplify completion cache and matcher filtering
- Improve LSP completion item parsing with safer fallbacks
- Modernize typing (Python 3.10 union syntax)
- Remove unused imports and dead code
- Use GLib.idle_add for safe UI scrolling operations
- Minor comment and spelling fixes

plugins/code/ui/lsp_manager/handlers/registry.py

@@ -0,0 +1,49 @@
+# Python imports
+
+# Lib imports
+
+# Application imports
+from ..mixins.lsp_server_events_mixin import LSPServerEventsMixin
+
+from .base import BaseHandler
+from .default import DefaultHandler
+from .python import PythonHandler
+from .java import JavaHandler
+
+
+
+class HandlerRegistry(LSPServerEventsMixin):
+    def __init__(self):
+
+        self._instances: dict         = {}
+        self._lang_handlers: dict     = {
+            "default": DefaultHandler,
+            "python": PythonHandler,
+            "java": JavaHandler,
+        }
+
+
+    def _get_instance(self, handler_cls: type[BaseHandler]) -> BaseHandler:
+        if handler_cls in self._instances: return self._instances[handler_cls]
+
+        self._instances[handler_cls] = handler_cls()
+
+        return self._instances[handler_cls]
+
+    def register_handler(self, lang_id: str, handler_cls: type[BaseHandler]):
+        self._lang_handlers[lang_id] = handler_cls
+
+    def get_handler(self, lang_id: str = "", method: str = ""):
+        handler_cls = self._lang_handlers.get(
+            lang_id, self._lang_handlers.get("default", DefaultHandler)
+        )
+        
+        if not handler_cls: return None
+
+        return self._get_instance(handler_cls)
+
+    def close_handler(self, lang_id: str):
+        if not lang_id in self._lang_handlers: return
+
+        handler_cls = self._lang_handlers[lang_id]
+        self._instances.pop(handler_cls, None)