Correct the version and make the config merge deeply

The package version had been left at the scaffolded 0.1.0 while the released
tag was v5.4.0. Nothing in the code chose 0.1.0 -- it was npm-init's equivalent,
never updated -- and it made every version comparison meaningless: the window
title, the About dialog and the update check all read it.

ConfigManager merged a stored config over the defaults with dict.update(),
which is shallow. A config written by an older build carries partial "player"
and "feed" objects, and a shallow update replaces the whole nested default with
the partial one, so keys added since came back missing. The `or 15` and
`or "auto"` fallbacks at the call sites were load-bearing because of it. The
merge is now recursive, and keys present only in the stored file are kept so a
downgrade cannot destroy settings.

Configs now carry a config_version. A file written before 5.4.0 -- including
one inherited from an upstream YTSage install -- has its stored
check_app_updates cleared once, because that setting used to point at PyPI's
`ytsage` package and oop7/YTSage's releases, neither of which is this program.

The settings tab read a missing check_app_updates as enabled and persisted that
reading on OK, so merely opening Custom Options turned the checker back on.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

ytsage/gui/ytsage_gui_dialogs/ytsage_dialogs_updater.py

@@ -688,9 +688,11 @@ class UpdaterTabWidget(QWidget):
             beta_enabled = ConfigManager.get("check_beta_updates") or False
             self.beta_updates_checkbox.setChecked(beta_enabled)
 
-            # Load app update checker setting (default enabled for older configs)
+            # Load app update checker setting. `is not False` would have read a
+            # missing key as enabled, and since this dialog persists the value
+            # unconditionally on OK, merely opening it re-enabled the checker.
             app_updates_enabled = ConfigManager.get("check_app_updates")
-            self.app_updates_checkbox.setChecked(app_updates_enabled is not False)
+            self.app_updates_checkbox.setChecked(bool(app_updates_enabled))
             
             # Set current selection based on saved settings
             current_frequency = auto_settings["frequency"]