Add option to use random numbers as the word separator in passphrase generator

**Is your feature request related to a problem? Please describe.**
Currently the generated passphrase word separator can be set to a static value. Some other password managers allow using random numbers as the word separator. This can add a bit more entropy while still retaining the easy-to-type/remember property of passphrases.

**Describe the solution you'd like**
When generating a passphrase, expose a choice between a static word separator and "random numbers" as the word separator.

**Describe alternatives you've considered**
N/A

**Additional context**
N/A

No file, test, or entry point is named. Start by locating the passphrase generator and the current static-separator setting, then trace how that setting reaches the generation UI. Done means users can choose random numbers instead of a static separator and generated passphrases use that choice consistently.

Written by the indexing model from the issue text.