* Made countdown colors configurable.
* Added support for selecting the countdown display type (numeric value or cake-style).
* Wired the validity countdown switch to disable color pickers when “show countdown as seconds” is enabled, and stored those widgets in the settings state for reuse in callbacks.
* Added a dedicated handler to update color picker sensitivity whenever the display mode switch changes (including on dialog initialization).
* Added persistence for tree view column widths by loading saved widths on startup and saving current widths to the configuration on shutdown.
* Renamed the “OTP Value” column header to “OTP” and tagged columns with IDs to support width tracking.
* Added polished empty-state screens with direct call-to-action buttons.
* Improved consistency and clarity across menus, headers, and dialogs.
* Enhanced OTP list readability with resizable columns, ellipsized labels, and monospace formatting.
* Replaced the validity text column with a progress bar showing remaining TOTP time.
* Switched visual indicators from bar-based to filled pie charts for clearer status at a glance.
* Improved CLI usability and feedback.
* Refactored the codebase to follow proper GTK coding patterns and lifecycle management.
* Removed obsolete option-migration logic.
* Added an explicit shutdown event.
* Hardened shutdown cleanup to safely handle partially initialized components, avoiding GTK critical warnings while still persisting window state when possible.
OBS-URL: https://build.opensuse.org/package/show/GNOME:Apps/otpclient?expand=0&rev=90
