Description incorrect/not UI editable (simple fix)

## Describe the bug
Can't edit the description in the UI, doesn't pick up the variables from .env

## To Reproduce
Go through setup, provide description for the site, it will keep the pixelfed defaults.
Use the settings blade, provide the description, it will revert the moment you change blades.

## Expected behavior
It should update when saved, or at least take the value from .env

## Simple short-term fix:
The environmental vars it's using are *actually* these two:
PF_SHORT_DESCRIPTION="your desc"
PF_DESCRIPTION="your longer desc"

And not these two:
INSTANCE_DESCRIPTION=""
SHORT_DESCRIPTION=""

Start with the setup flow and settings blade described in the reproduction steps, then trace where the site description environment variables are read and saved. Verify which variable names are used and confirm that saving a description persists or that the documented .env values are applied after setup.

Written by the indexing model from the issue text.