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/tests/stage.go

@@ -16,11 +16,30 @@ import (
 //   - Message is only used on failure; the UI displays it in the log.
 //   - Extras is merged into the posted summary so stages can add
 //     their own shape (e.g. Storage returns per-disk probe results).
+//   - SubSteps carries agent-authored sub-step rows (CPU/Memory passes,
+//     per-disk SMART, per-device GPU, …). Empty for stages with no
+//     natural breakdown; persisted verbatim by the /result handler.
 type Outcome struct {
-	Passed  bool
-	Message string
-	Summary string         // short human-readable one-liner
-	Extras  map[string]any // merged into posted summary JSON
+	Passed   bool
+	Message  string
+	Summary  string           // short human-readable one-liner
+	Extras   map[string]any   // merged into posted summary JSON
+	SubSteps []SubStepReport  // agent-authored granular rows
+}
+
+// SubStepReport is one entry a stage contributes to its sub-step list.
+// Ordinal is assigned in the order entries appear in the slice — the
+// agent shouldn't set it manually. State is derived from Passed/Skipped
+// the same way Outcome is: Skipped wins if set, else Passed ? passed :
+// failed. StartedAt/CompletedAt are required so the UI can order rows
+// and slice the stage log by time window.
+type SubStepReport struct {
+	Name        string
+	Passed      bool
+	Skipped     bool
+	StartedAt   time.Time
+	CompletedAt time.Time
+	SummaryJSON json.RawMessage
 }
 
 // MarshalSummary builds the summary JSON body POSTed to /result.