debug: force Metadata v0 to fix kafka-go readPartitions issue

- Set max_version=0 for Metadata API to avoid kafka-go parsing issues
- Add detailed debugging for Metadata v0 responses
- Improve SyncGroup debug messages
- Root cause: kafka-go's readPartitions fails with v1+ but works with v0
- Issue: kafka-go still not calling SyncGroup after successful readPartitions

Progress:
✅ Produce phase working perfectly
✅ JoinGroup working with leader election
✅ Metadata v0 working (no more 'multiple Read calls' error)
❌ SyncGroup never called - investigating assignTopicPartitions phase

weed/mq/kafka/protocol/handler.go

@@ -235,8 +235,7 @@ func (h *Handler) HandleConn(conn net.Conn) error {
 				fmt.Printf("DEBUG: JoinGroup response hex dump (%d bytes): %x\n", len(response), response)
 			}
 		case 14: // SyncGroup
-			fmt.Printf("DEBUG: *** SYNCGROUP REQUEST RECEIVED *** Correlation: %d, Version: %d\n", correlationID, apiVersion)
-			fmt.Printf("DEBUG: *** THIS IS CRITICAL - SYNCGROUP WAS CALLED! ***\n")
+			fmt.Printf("DEBUG: *** 🎉 SYNCGROUP API CALLED! Version: %d, Correlation: %d ***\n", apiVersion, correlationID)
 			response, err = h.handleSyncGroup(correlationID, apiVersion, messageBuf[8:]) // skip header
 			if err != nil {
 				fmt.Printf("DEBUG: SyncGroup error: %v\n", err)
@@ -314,10 +313,10 @@ func (h *Handler) handleApiVersions(correlationID uint32) ([]byte, error) {
 	response = append(response, 0, 3)  // max version 3
 
 	// API Key 3 (Metadata): api_key(2) + min_version(2) + max_version(2)
-	// Advertise Metadata v7 for Kafka 2.1+ compatibility
+	// Force kafka-go to use v0 to avoid readPartitions parsing issues
 	response = append(response, 0, 3) // API key 3
 	response = append(response, 0, 0) // min version 0
-	response = append(response, 0, 7) // max version 7
+	response = append(response, 0, 0) // max version 0
 
 	// API Key 2 (ListOffsets): api_key(2) + min_version(2) + max_version(2)
 	response = append(response, 0, 2) // API key 2
@@ -476,6 +475,14 @@ func (h *Handler) HandleMetadataV0(correlationID uint32, requestBody []byte) ([]
 	}
 
 	fmt.Printf("DEBUG: Metadata v0 response for %d topics: %v\n", len(topicsToReturn), topicsToReturn)
+	fmt.Printf("DEBUG: *** METADATA v0 RESPONSE DETAILS ***\n")
+	fmt.Printf("DEBUG: Response size: %d bytes\n", len(response))
+	fmt.Printf("DEBUG: Broker: %s:%d\n", h.brokerHost, h.brokerPort)
+	fmt.Printf("DEBUG: Topics: %v\n", topicsToReturn)
+	for i, topic := range topicsToReturn {
+		fmt.Printf("DEBUG: Topic[%d]: %s (1 partition)\n", i, topic)
+	}
+	fmt.Printf("DEBUG: *** END METADATA v0 RESPONSE ***\n")
 	return response, nil
 }