[REQ] Support multiple default passwords presets

Is your feature request related to a problem? Please describe

Keka currently only supports a single password in Preferences, used for both compression and extraction.

Describe the solution you'd like

Let Keka store a list of saved passwords instead of just one:

• When extracting, Keka automatically tries each saved password in the list until one works, without prompting.
• When compressing, the password field is pre-filled with the default password, but also shows a dropdown listing all saved passwords, so the user can quickly switch to a different one for that specific archive.

Describe alternatives you've considered

Manually switching the single default password depending on the task.