add "deactivate" button

DataGrip has a button that they call "deactivate", which drops the connection to the database but doesn't affect the UI. You can still edit/view queries you're editing and tables that you've already opened. If you try to do something that requires a connection, it will automatically try to reconnect.

It's helpful in my workflow, because I routinely destroy my local db, and migrate and seed it from scratch. If Postico is still holding a connection, dropping the database waits/fails until I switch to Postico, click the disconnect button, but then kicks me out to the menu, and I need to click connect again. With DataGrip, I can just use the keyboard shortcut and it keeps everything else open so I don't have to manually reconnect.

It's a very small thing, but I've been missing it since I switched to Postico. 😄

The issue names no files, tests, or entry points. Start by tracing Postico’s existing disconnect control and connection lifecycle, then determine how a deactivate action can preserve open queries and tables while reconnecting when needed. Done means the database connection can be dropped without closing the current UI, and connection-dependent actions trigger reconnection.

Written by the indexing model from the issue text.