Add activity log system for provisioning lifecycle visibility

Hosts stuck in states like pxe_ready had zero visibility into why.
This adds a persistent activity log that records every meaningful
step (state transitions, PXE events, cluster join stages, failures)
and surfaces it on the host detail page with live SSE updates.
Includes a stuck-detection warning banner when a host sits in
pxe_ready for >10 minutes with no iPXE request.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/api/render.go

@@ -5,6 +5,7 @@ import (
 	"html"
 	"net/http"
 	"strings"
+	"time"
 
 	"provisioning/internal/model"
 )
@@ -83,7 +84,7 @@ func hostFormPage(types []string, errMsg string, prefill *model.Host) string {
 	`, errHTML, hostname, mac, opts.String(), notes))
 }
 
-func hostDetailPage(h *model.Host, ops []model.Operation) string {
+func hostDetailPage(h *model.Host, ops []model.Operation, activity []model.ActivityEntry) string {
 	stateClass := stateColor(h.State)
 	led := ledClass(h.State)
 	canRebuild := h.State == model.StateRegistered || h.State == model.StateReady || h.State == model.StateFailed
@@ -113,12 +114,29 @@ func hostDetailPage(h *model.Host, ops []model.Operation) string {
 		ip = "—"
 	}
 
+	var stuckWarning string
+	if h.State == model.StatePXEReady && time.Since(h.UpdatedAt) > 10*time.Minute {
+		mins := int(time.Since(h.UpdatedAt).Minutes())
+		stuckWarning = fmt.Sprintf(`<div class="stuck-warning">Host has been in PXE_READY for %d minutes with no iPXE request. This usually means the host failed to PXE boot — check secure boot settings, network connectivity, and BIOS boot order.</div>`, mins)
+	}
+
+	var activityHTML strings.Builder
+	for _, e := range activity {
+		activityHTML.WriteString(fmt.Sprintf(
+			`<div class="log-entry log-%s"><span class="log-time">%s</span><span class="log-source">%s</span><span class="log-msg">%s</span></div>`,
+			e.Level, e.CreatedAt.Format("15:04"), html.EscapeString(e.Source), html.EscapeString(e.Message)))
+	}
+	if len(activity) == 0 {
+		activityHTML.WriteString(`<p class="empty">No activity recorded yet.</p>`)
+	}
+
 	return layout(h.Hostname, fmt.Sprintf(`
 		<div class="host-header">
 			<span class="led led-lg %s"></span>
 			<h2 style="margin-bottom:0">%s</h2>
 			<span class="badge %s">%s</span>
 		</div>
+		%s
 		<div class="panel">
 			<table class="detail-table">
 				<tr><th>MAC</th><td>%s</td></tr>
@@ -135,7 +153,15 @@ func hostDetailPage(h *model.Host, ops []model.Operation) string {
 				<tbody>%s</tbody>
 			</table>
 		</div>
-	`, led, html.EscapeString(h.Hostname), stateClass, h.State, h.MAC, h.ServerType, ip, html.EscapeString(h.Notes), actions.String(), opsHTML.String()))
+		<h3>Activity Log</h3>
+		<div class="panel">
+			<div class="activity-log" id="activity-log" data-host-id="%d">%s</div>
+		</div>
+	`, led, html.EscapeString(h.Hostname), stateClass, h.State,
+		stuckWarning,
+		h.MAC, h.ServerType, ip, html.EscapeString(h.Notes), actions.String(),
+		opsHTML.String(),
+		h.ID, activityHTML.String()))
 }
 
 func imagesPage(images []model.Image) string {