Track alert delivery health at runtime:
- AlertHealth struct: LastSendAt, LastSendOK, LastError, SendCount, FailCount
- triggerAlert records success/failure after each Send()
- Health data exposed via GetAlertHealth() for TUI
Alerts tab enriched:
- Health dot column: green (OK), red (failed), gray (never sent)
- LAST SENT column: relative time ("2m ago", "never")
- [t] key sends test notification through selected channel
Inspired by Grafana's contact point health columns.
lerko
0aa2f9cd8a