fix: Wait for volume assignment readiness before running Parquet tests

The test-implicit-dir-with-server test was failing with an Internal Error
because volume assignment was not ready when tests started. This fix adds
a check that attempts a volume assignment and waits for it to succeed
before proceeding with tests.

This ensures that:
1. Volume servers are registered with the master
2. Volume growth is triggered if needed
3. The system can successfully assign volumes for writes

Fixes the timeout issue where boto3 would retry 4 times and fail with
'We encountered an internal error, please try again.'

test/s3/parquet/Makefile

@@ -151,6 +151,31 @@ start-seaweedfs-ci: check-binary
 	# Additional wait for filer gRPC to be ready
 	@echo "$(YELLOW)Waiting for filer gRPC to be ready...$(NC)"
 	@sleep 2
+	
+	# Wait for volume server to register with master and ensure volume assignment works
+	@echo "$(YELLOW)Waiting for volume assignment to be ready...$(NC)"
+	@for i in $$(seq 1 30); do \
+		ASSIGN_RESULT=$$(curl -s "http://localhost:$(MASTER_PORT)/dir/assign?count=1" 2>/dev/null); \
+		if echo "$$ASSIGN_RESULT" | grep -q '"fid"'; then \
+			echo "$(GREEN)Volume assignment is ready$(NC)"; \
+			break; \
+		fi; \
+		if [ $$i -eq 30 ]; then \
+			echo "$(RED)Volume assignment not ready after 30 seconds$(NC)"; \
+			echo "=== Last assign attempt ==="; \
+			echo "$$ASSIGN_RESULT"; \
+			echo "=== Master Status ==="; \
+			curl -s "http://localhost:$(MASTER_PORT)/dir/status" 2>/dev/null || echo "Failed to get master status"; \
+			echo "=== Master Logs ==="; \
+			tail -50 /tmp/seaweedfs-parquet-master.log 2>/dev/null || echo "No master log"; \
+			echo "=== Volume Logs ==="; \
+			tail -50 /tmp/seaweedfs-parquet-volume.log 2>/dev/null || echo "No volume log"; \
+			exit 1; \
+		fi; \
+		echo "Waiting for volume assignment... ($$i/30)"; \
+		sleep 1; \
+	done
+	
 	@echo "$(GREEN)SeaweedFS server started successfully for Parquet testing$(NC)"
 	@echo "Master: http://localhost:$(MASTER_PORT)"
 	@echo "Volume: http://localhost:$(VOLUME_PORT)"