test(networking): Add Tier 2/3 tests for Socket Relay

Tier 2 Integration Tests (4 tests):
- testWaitForSocketTimeout: Verifies timeout handling
- testWaitForSocketSuccess: Tests socket detection with nc
- testPortCollisionHandling: Tests port conflict detection
- testMultipleConcurrentConnections: Tests 5 concurrent TCP connections

Tier 3 E2E Tests (2 tests):
- testContainerComposeBinaryExists: Binary location verification
- testFullStackWithRelay: Placeholder for container runtime test

All 9 tests passing:
- 3 unit tests (Tier 1)
- 4 integration tests (Tier 2)
- 2 E2E tests (Tier 3 - 1 skipped, requires container runtime)

Part of Plan 75: Swift-Native Socket Relay

Author: explicitcontextualunderstanding