refactor(command-system): standardize command execution with *args/**kwargs

- Refactor exec_with_args to use *args/**kwargs instead of tuple arguments
- Add *args/**kwargs to all command execute functions for consistency
- Support multiple key bindings per command in registration
- Add character-based key binding support via get_char() in KeyMapper
- Make execute_plugin async and use asyncio.run for plugin execution
- Use MIME type from Gio content_type instead of language for ftype

src/libs/dto/code/register_command_event.py

@@ -14,7 +14,7 @@ from ..base_event import BaseEvent
 
 @dataclass
 class RegisterCommandEvent(BaseEvent):
-    command_name: str = ""
-    command: callable = None
-    binding_mode: str = ""
-    binding: str      = ""
+    command_name: str    = ""
+    command: callable    = None
+    binding_mode: str    = ""
+    binding: str or list = ""