refactor(code): move temp cut buffer feature and clean up related code

- Moved cut_to_temp_buffer and paste_temp_buffer commands to plugin
- Remove temporary cut buffer logic from SourceView
- Remove related keybindings (Ctrl+K / Ctrl+U)
- Fix word-end detection in ProviderResponseCacheBase to avoid extending past line end
- Improve completion controller to support RequestCompletionEvent with optional provider filtering
- Add GetActiveViewEvent handling in SourceViewsController
- Ensure view scrolls to cursor after buffer switch via GLib.idle_add
- Emit focus-in-event after DnD file load to restore focus behavior
- Prevent "buffer" pseudo-path from interfering with loaded file filtering
- Remove obsolete AGENTS.md from LSP manager plugin

user_config/usr/share/app_name/code-key-bindings.json

@@ -15,18 +15,12 @@
         "zoom_out": {
             "held": "<Control>minus"
         },
-        "cut_to_temp_buffer": {
-            "held": "<Control>k"
-        },
         "duplicate_line": {
             "held": "<Control>d"
         },
         "go_to": {
             "released": "<Control>g"
         },
-        "paste_temp_buffer": {
-            "held": "<Control>u"
-        },
         "new_file": {
             "released": "<Control>t"
         },