Default generic_mode to True; preserve explicit False

Set the default generic_mode to True in the config manager and update GUI initialization to distinguish between a missing config and an explicit False. Replace usages of `ConfigManager.get(... ) or False` with a None check so that an explicit False value is respected. Changes made in ytsage/utils/ytsage_config_manager.py and GUI initializers in ytsage/gui/ytsage_gui_main.py and ytsage/gui/ytsage_gui_dialogs/ytsage_dialogs_settings.py.

ytsage/utils/ytsage_config_manager.py

@@ -71,7 +71,7 @@ class ConfigManager:
     _settings: Dict[str, Any] = {}
     _default_config: Dict[str, Any] = {
         "download_path": str(USER_HOME_DIR / "Downloads"),
-        "generic_mode": False,
+        "generic_mode": True,
         "speed_limit_value": None,
         "speed_limit_unit_index": 0,
         "cookie_source": "browser",  # "browser" or "file"