ui: stream host-detail fragments over SSE so the page updates live

The detail page was only partly live: Pipeline + LogTabs subscribed to
SSE, but the summary header, actions row, spec-diffs list and hold-key
block all froze at page-load and required a manual refresh to catch up
with state changes.

Extract each of those four regions into its own named templ component
with a stable id and sse-swap target, add Render*String helpers so the
orchestrator can publish pre-rendered fragments, and register a
HostDetailRenderer alongside the existing Tile/Pipeline renderers.
PublishHostDetail is folded into publishTileUpdate so every call site
that already refreshes a tile now also refreshes the detail page —
keeps the fan-out honest without scattering new publish calls.

The empty-state wrappers for spec-diffs and hold are load-bearing:
without the <section id=... sse-swap=...> present at initial GET, the
first live event after SpecValidate or Hold writes would have no DOM
node to swap into.

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

cmd/vetting/main.go

@@ -109,6 +109,27 @@ func main() {
 		PublicURL: cfg.Server.PublicURL,
 	}
 
+	// Inject the host-detail fragment renderer. The closure reuses
+	// LoadHostDetailData so the SSE-pushed HTML matches an identical
+	// reload-rendered page byte-for-byte, then hands each region to
+	// its Render*String helper.
+	orchestrator.HostDetailRenderer = func(ctx context.Context, hostID int64) (orchestrator.HostDetailFragments, bool) {
+		d, err := ui.LoadHostDetailData(ctx, hostID)
+		if err != nil {
+			return orchestrator.HostDetailFragments{}, false
+		}
+		f := orchestrator.HostDetailFragments{
+			Summary:   templates.RenderDetailSummaryString(d),
+			Actions:   templates.RenderDetailActionsString(d),
+			SpecDiffs: templates.RenderDetailSpecDiffsString(d),
+			Hold:      templates.RenderDetailHoldString(d),
+		}
+		if d.Tile.Latest != nil {
+			f.LatestRunID = d.Tile.Latest.ID
+		}
+		return f, true
+	}
+
 	agentAPI := &api.Agent{
 		Hosts:           hostStore,
 		Runs:            runStore,