database/middleware: don't use sql.Conn in WithTx

We can just use sql.DB instead of sql.Conn here. Simplifies the
code and reduces the risk of getting "bad connection" errors.

database/middleware: do not recover/panic in defer

defer always runs after a panic. There is no need to recover and
re-panic, we can just unconditionally tx.Rollback() (it will
silently error out if the transaction has already been committed or
rolled back).

This fixes the stack trace of the panic being incorrect. It points
to this function instead of the real culprit.

database: panic on errors from Commit/Rollback

The previous change would eat the error from fn(tx); in truth we should
ensure that it is returned to the caller. This panics instead if an
error occurs during Commit or Rollback. I'm not sure of what scenarios
would cause this to occur, but they all probably deserve further
investigation - a panic will raise it to our attention.

database: handle Commit/Rollback errors

database.WithTx: rollback if func returns error

Previously, this only rolled back if the called function panicked. This
updates it to also roll back if the called function returns an error.

Expand context for work queues

Add basic auth tests

Import GQL server interfaces from gql.sr.ht