feat: add test isolation scripts with dynamic port discovery

- Add get-test-instance-id.sh for branch-based container isolation
- Add run-integration-tests.sh for full test lifecycle management
- Update integration tests to read service URLs from environment
  variables (GRIST_MCP_URL, MOCK_GRIST_URL) with fallback defaults

scripts/get-test-instance-id.sh

@@ -0,0 +1,7 @@
+#!/bin/bash
+# scripts/get-test-instance-id.sh
+# Generate a unique instance ID from git branch for parallel test isolation
+
+BRANCH=$(git rev-parse --abbrev-ref HEAD 2>/dev/null || echo "unknown")
+# Sanitize: replace non-alphanumeric with dash, limit length
+echo "$BRANCH" | sed 's/[^a-zA-Z0-9]/-/g' | cut -c1-20