Feat v0.6.4 admin health/metrics tab + cluster merge

Admin Health tab under Monitoring with auto-refreshing runtime, DB,
cluster, and extension metrics panels. New GET /api/v1/admin/metrics
endpoint. Fattened heartbeat JSONB with stack, GC CPU%, extension
count, sandbox stats, trigger fires. Sandbox runner and trigger engine
now track cumulative execution counters. Event bus tracks publish/deliver
counts. Health endpoints consolidated via shared builder. Block renderers
(mermaid, katex, csv-table, diff-viewer) no longer require chat.
cluster-dashboard package retired — merged into admin Health tab.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

server/cluster/registry.go

@@ -34,6 +34,26 @@ type Registry struct {
 	startTime time.Time
 	stopCh    chan struct{}
 	wg        sync.WaitGroup
+
+	// Optional callbacks — set after construction via setters.
+	sandboxStats   func() (exec, errors uint64, avgMs float64)
+	triggerFires   func() int64
+	extensionCount func() int
+}
+
+// SetSandboxStats registers a callback for sandbox execution counters.
+func (r *Registry) SetSandboxStats(fn func() (uint64, uint64, float64)) {
+	r.sandboxStats = fn
+}
+
+// SetTriggerFireCount registers a callback for trigger fire count.
+func (r *Registry) SetTriggerFireCount(fn func() int64) {
+	r.triggerFires = fn
+}
+
+// SetExtensionCount registers a callback for active extension count.
+func (r *Registry) SetExtensionCount(fn func() int) {
+	r.extensionCount = fn
 }
 
 // NewRegistry creates a cluster registry instance.
@@ -129,13 +149,28 @@ func (r *Registry) collectStats() json.RawMessage {
 	runtime.ReadMemStats(&m)
 
 	stats := map[string]any{
-		"goroutines":  runtime.NumGoroutine(),
-		"heap_alloc":  m.HeapAlloc,
-		"heap_sys":    m.HeapSys,
-		"gc_cycles":   m.NumGC,
-		"gc_pause_ns": m.PauseNs[(m.NumGC+255)%256],
-		"uptime_sec":  time.Since(r.startTime).Seconds(),
-		"ws_clients":  r.hub.ConnCount(),
+		"goroutines":    runtime.NumGoroutine(),
+		"heap_alloc":    m.HeapAlloc,
+		"heap_sys":      m.HeapSys,
+		"stack_in_use":  m.StackInuse,
+		"gc_cycles":     m.NumGC,
+		"gc_pause_ns":   m.PauseNs[(m.NumGC+255)%256],
+		"gc_cpu_pct":    m.GCCPUFraction * 100,
+		"uptime_sec":    time.Since(r.startTime).Seconds(),
+		"ws_clients":    r.hub.ConnCount(),
+	}
+
+	if r.extensionCount != nil {
+		stats["extensions_loaded"] = r.extensionCount()
+	}
+	if r.sandboxStats != nil {
+		exec, errors, avgMs := r.sandboxStats()
+		stats["starlark_exec_total"] = exec
+		stats["starlark_errors_total"] = errors
+		stats["starlark_avg_duration_ms"] = avgMs
+	}
+	if r.triggerFires != nil {
+		stats["trigger_fires_total"] = r.triggerFires()
 	}
 
 	data, _ := json.Marshal(stats)