Add handler queue metrics to status page

- Add GetHandlerStats() method to streamer to expose handler metrics
- Include queue length/capacity, processed/dropped counts, timing stats
- Update API to include handler_stats in response
- Add dynamic handler stats display to status page HTML
- Shows separate status box for each handler with all metrics

internal/streamer/streamer.go

@@ -195,6 +195,57 @@ func (s *Streamer) GetMetrics() metrics.StreamMetrics {
 	return s.metrics.GetStreamMetrics()
 }
 
+// HandlerStats represents metrics for a single handler
+type HandlerStats struct {
+	Name           string
+	QueueLength    int
+	QueueCapacity  int
+	ProcessedCount uint64
+	DroppedCount   uint64
+	AvgProcessTime time.Duration
+	MinProcessTime time.Duration
+	MaxProcessTime time.Duration
+}
+
+// GetHandlerStats returns current handler statistics
+func (s *Streamer) GetHandlerStats() []HandlerStats {
+	s.mu.RLock()
+	defer s.mu.RUnlock()
+
+	stats := make([]HandlerStats, 0, len(s.handlers))
+
+	for _, info := range s.handlers {
+		info.metrics.mu.Lock()
+
+		hs := HandlerStats{
+			Name:           fmt.Sprintf("%T", info.handler),
+			QueueLength:    len(info.queue),
+			QueueCapacity:  cap(info.queue),
+			ProcessedCount: info.metrics.processedCount,
+			DroppedCount:   info.metrics.droppedCount,
+			MinProcessTime: info.metrics.minTime,
+			MaxProcessTime: info.metrics.maxTime,
+		}
+
+		// Calculate average time
+		if info.metrics.processedCount > 0 {
+			processedCount := info.metrics.processedCount
+			const maxInt64 = 1<<63 - 1
+			if processedCount > maxInt64 {
+				processedCount = maxInt64
+			}
+			//nolint:gosec // processedCount is explicitly bounded above
+			hs.AvgProcessTime = info.metrics.totalTime / time.Duration(processedCount)
+		}
+
+		info.metrics.mu.Unlock()
+
+		stats = append(stats, hs)
+	}
+
+	return stats
+}
+
 // GetDroppedMessages returns the total number of dropped messages
 func (s *Streamer) GetDroppedMessages() uint64 {
 	return atomic.LoadUint64(&s.totalDropped)