- Expand ft601_be from [1:0] to [3:0] across RTL, top-level, testbenches,
and XDC (uncomment be[2:3] pin assignments B21/A21)
- Fix NCO XSim testbench: correct reset check (0x7FFF not 0), add pipeline
warmup and sample skip for DSP48E1 quadrature test
- All local regression tests pass (39/39 USB, 10/10 integration, all co-sim)