ui: keep detail-page SSE swaps live after the first outerHTML replace

Pipeline fragment payload was a bare <div class=pipeline>, but the
sse-swap=pipeline-N wrapper lived only in the page shell. The first
outerHTML swap destroyed the wrapper, so every subsequent pipeline
event had nothing to target — forcing a manual refresh. RenderPipelineString
now emits the full <section id=pipeline-N sse-swap=... hx-swap=outerHTML>
wrapper, used from both the shell and the orchestrator publish path.

Also drop the red-bar styling from the empty DetailHold placeholder:
the wrapper's detail-hold class was painting an unconditional red band
between Pipeline and Actions whenever no hold was active.

internal/web/templates/pipeline.templ

@@ -280,11 +280,35 @@ templ Pipeline(nodes []PipelineNode) {
 	</div>
 }
 
+// PipelineSection wraps Pipeline in the same <section id=pipeline-N
+// sse-swap=pipeline-N hx-swap=outerHTML> the runner targets. Used both
+// from the initial detail-page shell and from RenderPipelineString so
+// the wrapper is present on the wire and after every SSE swap — without
+// this, the first outerHTML swap would replace the section with a bare
+// <div class=pipeline>, wiping out the sse-swap attribute and freezing
+// the pipeline until full page reload.
+templ PipelineSection(run *model.Run, nodes []PipelineNode) {
+	<section
+		id={ fmt.Sprintf("pipeline-%d", run.ID) }
+		class="detail-section"
+		sse-swap={ fmt.Sprintf("pipeline-%d", run.ID) }
+		hx-swap="outerHTML"
+	>
+		<h2>Pipeline</h2>
+		@Pipeline(nodes)
+	</section>
+}
+
 // RenderPipelineString is the one-shot renderer the orchestrator
 // registers at startup so it can publish pipeline fragments over SSE
-// without pulling in the template package directly.
+// without pulling in the template package directly. Returns the full
+// PipelineSection wrapper so repeat outerHTML swaps preserve the
+// sse-swap target.
 func RenderPipelineString(run *model.Run, stages []model.Stage) string {
+	if run == nil {
+		return ""
+	}
 	var buf bytes.Buffer
-	_ = Pipeline(BuildPipeline(run, stages)).Render(context.Background(), &buf)
+	_ = PipelineSection(run, BuildPipeline(run, stages)).Render(context.Background(), &buf)
 	return buf.String()
 }