Add Windows Named Pipe transport

[kengwang]

Summary

• make authenticated Windows Named Pipes the default bridge transport
• retain loopback TCP as an explicit compatibility mode via BN_BRIDGE_TRANSPORT
• add pipe registry discovery, retries, timeouts, concurrent server handling, and graceful shutdown
• update CLI endpoint reporting and bundled documentation

Tests

• uv run pytest
• 247 passed, 9 skipped on Windows