Adds the tests/harness helper package: address(), available(), reset(),
users(), smtp_provider() and mailbox_config().
Tests address mailboxes as harness.address("<test name>"), which slugs the name
under the RFC 2606 reserved harness.email-connect.test domain, so distinct test
names cannot collide and a stray send cannot leave the host. No provisioning
call is needed -- the auth-disabled harness creates the mailbox on first login.
reset() drops every user and message via GreenMail's service reset; the next
login recreates the mailbox empty. It is documented to run at test start so a
crashed test cannot leak state forward, and it is global, so resetting tests
cannot run in parallel against one harness.
Suite: 64 passed with the harness up, 61 passed + 3 skipped with it down.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
