feat(tui-go): health-checks pane

Surface the health subsystem (llama/event-store/disk probes) in the TUI,
mirroring the session-stats pane: ClientMessage.GetHealthChecks ->
ServerMessage.HealthChecks (health.checks, reuses HealthReport) ->
StreamQueries.healthChecks via HealthInspectionService; Go OverlayHealth on
key H + palette 'health checks', pull-based fetch, per-subject status with
degraded loud. Empty/disabled -> visible fallback (no blank/lie). Go+Kotlin
golden tests pin the wire contract field-for-field. Observability spec §4/§3.

apps/tui-go/internal/app/server.go

@@ -322,6 +322,9 @@ func (m *Model) applyServer(msg protocol.ServerMessage) {
 		if m.ideasIndex >= len(m.ideas) {
 			m.ideasIndex = 0
 		}
+	case protocol.TypeHealthChecks:
+		m.health = msg.Health
+		m.healthLoading = false
 	case protocol.TypeConfigSnapshot:
 		m.configFields = msg.ConfigFields
 		m.configRestart = msg.ConfigRestartRequired
@@ -367,7 +370,7 @@ func sessionIDOf(msg protocol.ServerMessage) string {
 		protocol.TypeWorkflowList, protocol.TypeRouterResponse,
 		protocol.TypeModelChanged, protocol.TypeModelList, protocol.TypeResourceStatus,
 		protocol.TypeArtifactList, protocol.TypeConfigSnapshot, protocol.TypeSessionStats,
-		protocol.TypeIdeaList:
+		protocol.TypeIdeaList, protocol.TypeHealthChecks:
 		return ""
 	default:
 		return msg.SessionID