feat(doctor): create a missing database from the finding

[geodro]

A site pointing at a MySQL or Postgres schema its engine does not hold was told to go and run lerd db:create, which made it the one finding on the doctor panel ending in a command to type somewhere else. The button it did carry ran the framework's migrate command, and that could never resolve it: migrations have nowhere to run until the database exists, so pressing it failed against the very thing the finding was about.

The finding creates the database now, from the dashboard and from lerd site:doctor --fix alike. Creating a schema happens in the engine's container rather than the site's, so it runs as a host action beside installing a service the site declares, and it resolves the missing set again on the way in so it can only ever create what the check reported, stopping at the first refusal rather than reporting a half done run as done. An engine that cannot be reached still produces no finding and no work.

A database that does not exist already suppresses the framework migration check, so the migrate button returns on the re-check that follows and the two steps stay in the order they have to happen in. The SQLite sibling is untouched: an absent or empty file is exactly what migrations do create.

Closes #1491