bc3a44beac
Propagate check failure reasons through the entire stack: - Checker captures specific errors (DNS, timeout, HTTP status, SSL, etc.) - Engine tracks LastError, StatusChangedAt, LastSuccessAt per monitor - State transitions persisted to new state_changes table - Detail panel shows error reason, HTTP code, state duration, last success time, and last 5 state change events - Monitor table shows inline error preview for DOWN services - Alert messages include error reason - Probe nodes forward error reasons to leader 15 files changed across models, checker, engine, store, TUI, and probes.