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>

agent/client.go

@@ -150,6 +150,19 @@ type ResultResponse struct {
 	NextState string `json:"next_state"`
 }
 
+// SubStepReport is the wire shape the agent POSTs inside /result for
+// each granular sub-step (CPU/Memory pass, per-disk SMART, per-device
+// GPU, …). Ordinal is assigned by the server in slice order; the agent
+// doesn't set it. Summary is opaque JSON the UI may render later.
+type SubStepReport struct {
+	Name        string          `json:"name"`
+	Passed      bool            `json:"passed"`
+	Skipped     bool            `json:"skipped,omitempty"`
+	StartedAt   string          `json:"started_at,omitempty"`
+	CompletedAt string          `json:"completed_at,omitempty"`
+	Summary     json.RawMessage `json:"summary,omitempty"`
+}
+
 type HoldResponse struct {
 	AuthorizedKey string `json:"authorized_key"`
 	RunID         int64  `json:"run_id"`