KeepSecret: UX Improvements and Feature Additions

KeepSecret is a modern password manager built using Qt/QML and Kirigami, but there are still a few areas that need improvements. For example, the sidebar currently appears even for users with a single wallet, which isn’t necessary. Features like import/export are missing, there’s no built-in password generator, and copied passwords stay in the clipboard without being cleared. Keyboard navigation is also incomplete, and there are some build warnings that is unresolved. This proposal addresses all these areas: completing the sidebar-hiding feature with correct page navigation, resolving outstanding build warnings, implementing import and export functionality, adding a password generator, improving keyboard-only navigation, implementing clipboard auto-clear after copying a password, and adding a close button for the entry detail panel.