Tests: notification pipeline (email + Prowl) is not tested end-to-end

[tkadauke]

Description

The notification system sends emails and Prowl push notifications when health checks change state. While mailer unit tests exist (spec/mailers/check_run_mailer_spec.rb), the notifier orchestration (lib/tiny_mon/notifier.rb, lib/tiny_mon/notification/) is not tested.

Critical untested behaviors:

• Is the notifier called after a check changes from success to failure?
• Is it called after failure → success recovery?
• Are notifications correctly scoped to account users who subscribed?
• Does notification failure (e.g., Prowl API down) prevent check_run from being saved?

Suggested approach

Add spec/lib/tiny_mon/notifier_spec.rb and ensure the mailer is called with the right arguments for state transitions. Use ActionMailer::Base test helpers and mock the Prowl HTTP call.

Effort: small