ui: GitHub-Actions-style detail page, sub-steps, mini-tile run-view

Reshapes the detail page into a run-view: hybrid horizontal pipeline
+ expanded active-step pane with sub-steps, a per-step log pane with
line-numbered permalinks and client-side search, and a runs-history
sidebar that navigates via ?run=N. Default step is server-picked
(running → failed → Reporting) so the operator lands on the thing
that's moving.

Adds a sub_steps table + SSE topic (substep-{run}-{stage}-{ordinal})
so per-disk and per-pass work (SMART, CPUStress CPU/RAM, Storage,
GPU) is visible in the UI instead of buried in stage summary JSON.
Agent emits sub-step reports from existing per-iteration loops.

Dashboard tiles become a mini run-view with a 9-dot step strip so
the operator reads run health across the whole grid at a glance.
Register page gets the same card shell + button styling.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

internal/orchestrator/runner.go

@@ -154,6 +154,25 @@ var TileRenderer func(ctx context.Context, host model.Host, latest *model.Run) s
 // orchestrator stays free of template imports.
 var PipelineRenderer func(run *model.Run, stages []model.Stage) string
 
+// SubStepRenderer renders a single sub-step row fragment. Fires on
+// every sub-step state transition (running → passed/failed) so the
+// detail page's `<div sse-swap="substep-{runID}-{stage}-{ordinal}">`
+// target updates without reloading.
+var SubStepRenderer func(ss model.SubStep) string
+
+// PublishSubStepUpdate broadcasts a single sub-step row. Callers give
+// the just-persisted SubStep; we render + fan out. Safe to call when
+// no renderer is wired; drops silently.
+func (r *Runner) PublishSubStepUpdate(ctx context.Context, ss model.SubStep) {
+	if SubStepRenderer == nil || r.EventHub == nil {
+		return
+	}
+	r.EventHub.Publish(events.Event{
+		Name:    fmt.Sprintf("substep-%d-%s-%d", ss.RunID, ss.StageName, ss.Ordinal),
+		Payload: SubStepRenderer(ss),
+	})
+}
+
 // HostDetailFragments is the pre-rendered bundle of HTML fragments a
 // single PublishHostDetail call broadcasts over SSE. Summary and Actions
 // are always set; SpecDiffs and Hold are empty strings when there is no