missing tile/overlap parameters for returning users

[ssube]

Returning users with some existing parameters in app state may see empty fields for the new UNet/VAE tile and overlap parameters, which causes an exception and prevents them from generating images. This is not an issue for new users because zustand provides them with the default state based on server parameters, only returning users with state from v0.10 or before.

Write a generic zustand state migration that will fill in any missing parameters using the server's defaults and bump the app's state version to match the server/release version.