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

src/core/widgets/code/command_system/commands/dnd_load_file_to_buffer.py

@@ -9,6 +9,7 @@ from gi.repository import GtkSource
 from gi.repository import Gtk
 from gi.repository import Gdk
 from gi.repository import Gio
+from gi.repository import GLib
 
 # Application imports
 from ..command_helpers import update_info_bar_if_focused
@@ -35,6 +36,10 @@ def execute(
     update_info_bar_if_focused(view.command, view)
     view.emit("focus-in-event", Gdk.Event())
 
-    buffer = view.get_buffer()
-    itr    = buffer.get_iter_at_mark( buffer.get_insert() )
-    view.scroll_to_iter(itr, 0.2, False, 0, 0)
+    def scroll_to_insert_itr(view):
+        buffer = view.get_buffer()
+        itr    = buffer.get_iter_at_mark( buffer.get_insert() )
+        view.scroll_to_iter(itr, 0.2, False, 0, 0)
+
+    GLib.idle_add(scroll_to_insert_itr, view)
+