engine: this GPU's own arithmetic and shared weight tiles as the builders' defaults

- layer_m.comp builds relaxed by default (M_RELAXED: f32 accumulators, paired FP8
  conversions, no activation table) with two windows per wave sharing weight tiles
  (WPW=2); M_EXACT=1 keeps NVIDIA's roundings, bit-identical to the CUDA path
- layer.comp reuses weight tiles across its waves (TPW=2 in the 32-channel layers)
- engine/rr/rr2_w.comp: one wave per window for preset F's dec0_0 and enc0, used by
  compile_rr2.py at the new default D4R_RR_RELAXED=3 (build_native_model.sh too);
  D4R_RR_FUSE=1 matches the reference's fused multiply-adds, ptx2rr.py --snorm16
- [Engine] Network defaults to vulkan; the HIP network is opt-in

engine/compile_k.py

@@ -186,7 +186,7 @@ def main():
     offsets = b''.join(params(ZeroShape(), e)[0][16:] for e in index.values())
     (a.output / 'offsets.bin').write_bytes(MAGIC + struct.pack('<II', 11, weights.stat().st_size) + offsets)
     for name, e in index.items():
-        subprocess.run(['glslangValidator', '-V', '--target-env', 'vulkan1.3', *defines(e),
+        subprocess.run(['glslangValidator', '-V', '--target-env', 'vulkan1.3', *defines(e, os.environ.get('K_DEFS_' + name.upper(), '').split()),   # per layer, e.g. K_DEFS_DEC0=-DTPW=2
                         str(HERE / 'layer.comp'), '-o', str(a.output / (name + '.spv'))], check=True)
     for name in ('input_k', 'output_k'):
         subprocess.run(['glslangValidator', '-V', '--target-env', 'vulkan1.3', *(['-DLDR=1'] if a.ldr else []),