email notifications and mobile apps are now working, and other minor updates

I rolled out some minor but important updates to the deployment cluster just now:

• email notifications are now enabled in production. let me know if this tanks performance. also we’re on a fairly limited email plan so I’ll post an update if we exceed its limits (which’ll break notifications again)
• we now have a staging deployment and a development deployment, which let me make these changes without taking production down
• lemmy-ui in production is now running in production mode, which should improve performance slightly
• late update: awful.systems now reports a correct lemmy backend version, so lemmy mobile apps should work. I confirmed that mlem on ios works, but let me know if jerboa or anything else is broken