Add sys import to test files and remove obsolete integration tests

- Add sys import to 29 test files across agent-coordinator, blockchain-event-bridge, blockchain-node, and coordinator-api
- Remove apps/blockchain-event-bridge/tests/test_integration.py (obsolete bridge integration tests)
- Remove apps/coordinator-api/tests/test_integration.py (obsolete API integration tests)
- Implement GPU registration in marketplace_gpu.py with GPURegistry model persistence

apps/coordinator-api/tests/test_agent_identity_sdk.py

@@ -2,6 +2,7 @@
 Tests for Agent Identity SDK
 Unit tests for the Agent Identity client and models
 """
+import sys
 
 import pytest
 import asyncio

apps/coordinator-api/tests/test_billing.py

@@ -2,6 +2,7 @@
 Tests for coordinator billing stubs: usage tracking, billing events, and tenant context.
 
 Uses lightweight in-memory mocks to avoid PostgreSQL/UUID dependencies.
+import sys
 """
 
 import asyncio

apps/coordinator-api/tests/test_health_comprehensive.py

@@ -2,6 +2,7 @@
 Comprehensive health endpoint tests for AITBC services
 
 Tests both internal service health and external marketplace health endpoints.
+import sys
 """
 
 import json

apps/coordinator-api/tests/test_integration_coordinator_api.py

@@ -2,6 +2,7 @@
 Basic integration tests for AITBC Coordinator API
 """
 
+import sys
 import pytest
 from fastapi.testclient import TestClient
 from unittest.mock import Mock, patch

apps/coordinator-api/tests/test_monitoring_metrics_alerting.py

@@ -2,6 +2,7 @@
 Unit tests for coordinator API metrics collection and alert delivery.
 Tests MetricsCollector, AlertDispatcher, and build_live_metrics_payload
 without requiring full app startup or database.
+import sys
 """
 
 import asyncio

apps/coordinator-api/tests/test_phase8_integration.py

@@ -2,6 +2,7 @@
 
 Env vars (set any that you want to exercise):
 
+import sys
 For optional endpoints:
   EXPLORER_API_URL   # e.g., http://127.0.0.1:8000/v1/explorer/blocks/head
   MARKET_STATS_URL   # e.g., http://127.0.0.1:8000/v1/marketplace/stats

apps/coordinator-api/tests/test_zk_integration.py

@@ -2,6 +2,7 @@
 
 Tests the end-to-end flow:
 1. Client submits a job with ZK proof requirement
+import sys
 2. Miner completes the job and generates a receipt
 3. Receipt is hashed and a ZK proof is generated (simulated)
 4. Proof is verified via the coordinator's confidential endpoint