Enhance e2e test with HTTP/2 and gRPC protocol coverage

- Add multi-domain test: whoami (HTTP/1.1) + grpcbin (gRPC/H2) backends
- Use ROUTING_MAP with SNI-based routing to test multi-backend support
- Add comma-separated ROUTING_MAP parsing (phala CLI -e flattens newlines)
- Test HTTP/2 against h2c-capable backend (grpcbin), not HTTP/1.1-only whoami
- Verify gRPC reflection, unary call, and SNI routing separation
- All 17 tests pass on live Phala CVM deployment

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: h4x3rotab