mq(kafka): force Metadata v0 for kafka-go compatibility - major breakthrough!

✅ SUCCESSES:
- Produce phase working perfectly with Metadata v0
- FindCoordinator working (consumer group discovery)
- JoinGroup working (member joins, becomes leader, deterministic IDs)
- Group state transitions: Empty → PreparingRebalance → CompletingRebalance
- Member ID reuse working correctly

🔍 CURRENT ISSUE:
- kafka-go makes repeated Metadata calls after JoinGroup
- SyncGroup not being called yet (expected after ReadPartitions)
- Consumer workflow: FindCoordinator → JoinGroup → Metadata (repeated) → ???

Next: Investigate why SyncGroup is not called after Metadata

weed/mq/kafka/protocol/handler.go

@@ -313,9 +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)
+	// TEMPORARY: Force v0 only until kafka-go compatibility issue is resolved
 	response = append(response, 0, 3) // API key 3
 	response = append(response, 0, 0) // min version 0
-	response = append(response, 0, 1) // max version 1
+	response = append(response, 0, 0) // max version 0 (force v0 for kafka-go compatibility)
 
 	// API Key 2 (ListOffsets): api_key(2) + min_version(2) + max_version(2)
 	response = append(response, 0, 2) // API key 2
@@ -1109,6 +1110,10 @@ func (h *Handler) handleMetadata(correlationID uint32, apiVersion uint16, reques
 		return h.HandleMetadataV0(correlationID, requestBody)
 	case 1:
 		return h.HandleMetadataV1(correlationID, requestBody)
+	case 2, 3, 4, 5, 6:
+		// For now, use v1 format for higher versions (kafka-go compatibility)
+		// TODO: Implement proper v2-v6 formats with additional fields
+		return h.HandleMetadataV1(correlationID, requestBody)
 	default:
 		return nil, fmt.Errorf("metadata version %d not implemented yet", apiVersion)
 	}