The appsettings example used AuthMode 'None', which the delivery code
(MailKitSmtpClientWrapper) rejects — only Basic and OAuth2 are valid.
Switch to a working Basic config with Credentials and TlsMode None, and
document that Server must be the container name scadalink-smtp when the
Notification Service runs inside the docker cluster.
Organize documentation by moving requirements (HighLevelReqs, Component-*,
lmxproxy_protocol) to docs/requirements/ and test infrastructure docs to
docs/test_infra/. Updates all cross-references in README, CLAUDE.md,
infra/README, component docs, and 23 plan files.
