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/orchestrator/runner.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"fmt"
 	"log"
+	"time"
 
 	"provisioning/internal/events"
 	"provisioning/internal/model"
@@ -12,10 +13,11 @@ import (
 )
 
 type Runner struct {
-	Hosts  *store.Hosts
-	Ops    *store.Operations
-	Locks  *store.Locks
-	Hub    *events.Hub
+	Hosts    *store.Hosts
+	Ops      *store.Operations
+	Locks    *store.Locks
+	Hub      *events.Hub
+	Activity *store.Activity
 }
 
 func (r *Runner) Transition(ctx context.Context, hostID int64, trigger statemachine.Trigger) (model.HostState, error) {
@@ -35,10 +37,12 @@ func (r *Runner) Transition(ctx context.Context, hostID int64, trigger statemach
 		Name:    "host.state_changed",
 		Payload: fmt.Sprintf(`{"host_id":%d,"old_state":"%s","new_state":"%s"}`, hostID, host.State, next),
 	})
+	r.LogActivity(ctx, hostID, model.LogInfo, "state", fmt.Sprintf("%s → %s", host.State, next))
 	return next, nil
 }
 
 func (r *Runner) FailHost(ctx context.Context, hostID int64, reason string) {
+	r.LogActivity(ctx, hostID, model.LogError, "orchestrator", "host failed: "+reason)
 	if _, err := r.Transition(ctx, hostID, statemachine.TriggerFailed); err != nil {
 		log.Printf("host %d: failed to transition to failed state: %v", hostID, err)
 		return
@@ -49,3 +53,16 @@ func (r *Runner) FailHost(ctx context.Context, hostID int64, reason string) {
 	}
 	_ = r.Locks.Release(ctx, hostID)
 }
+
+func (r *Runner) LogActivity(ctx context.Context, hostID int64, level model.LogLevel, source, message string) {
+	var opID int64
+	if op, err := r.Ops.GetActive(ctx, hostID); err == nil {
+		opID = op.ID
+	}
+	id, _ := r.Activity.Log(ctx, hostID, opID, level, source, message)
+	r.Hub.Publish(events.Event{
+		Name: "activity.logged",
+		Payload: fmt.Sprintf(`{"id":%d,"host_id":%d,"level":"%s","source":"%s","message":"%s","created_at":"%s"}`,
+			id, hostID, level, source, message, time.Now().UTC().Format(time.RFC3339)),
+	})
+}