[MUH] Fix three-layer disconnect — C++ headers are now the single source of truth

Problems fixed:
  1. gen_patch.py was reading .muh YAML (all nulls) instead of C++ headers.
     Now it parses bi100_* structs directly from tuning_*.cuh via regex,
     extracts constexpr values, and maps them to vllm injection points.
     Verified: 11 patches generated from 6 algorithms.

  2. C++ headers had no build system or tests.
     Added CMakeLists.txt (header-only library target) and compile_test.cpp.
     Verified: g++ -std=c++17 compiles all headers, 17/17 runtime checks pass.
     Also added cuda_compile_test.cu for when nvcc is available.

  3. baseline.muh had a tuning section full of nulls duplicating C++ values.
     Stripped to vllm launch config only. Tuning values live exclusively
     in muh/include/muh/tuning/tuning_*.cuh bi100_* structs.

  4. Fixed constexpr goto in tuning_scan.cuh (C++17 doesn't allow goto in
     constexpr; replaced with early-return + default: break pattern).

Data flow is now:
  tuning_*.cuh (bi100_* constexpr) ──→ gen_patch.py ──→ vllm patches
  baseline.muh (launch config)     ──→ gen_yaml.py  ──→ computility-run.yaml
  compile_test.cpp                 ──→ g++/nvcc     ──→ verify values are real

muh/test/cuda_compile_test.cu

@@ -0,0 +1,41 @@
+// muh/test/cuda_compile_test.cu — CUDA compilation test
+//
+// Verifies muh headers compile under nvcc/clang CUDA mode.
+// Does NOT require GPU execution — just compilation.
+
+#include "muh/muh.cuh"
+
+__global__ void dummy_kernel() {
+  // Instantiate policy selectors in device code to verify
+  // all constexpr paths compile on the device side
+  auto hw = muh::hardware_capability::bi_v100();
+
+  // Reduce
+  auto rp = muh::tuning::reduce::policy_selector{
+    .accum_t = muh::tuning::type_t::float32,
+    .operation_t = muh::tuning::op_kind_t::plus,
+    .offset_size = 4,
+    .accum_size = 4,
+  }(hw);
+  (void)rp;
+
+  // Topk
+  auto tp = muh::tuning::topk::policy_selector{.key_size = 2}(hw);
+  (void)tp;
+}
+
+int main() {
+  // Host-side test (same as compile_test.cpp core)
+  auto hw = muh::target_hw;
+
+  auto reduce_policy = muh::tuning::reduce::policy_selector{
+    .accum_t = muh::tuning::type_t::float32,
+    .operation_t = muh::tuning::op_kind_t::plus,
+    .offset_size = 4,
+    .accum_size = 4,
+  }(hw);
+
+  printf("CUDA compile test passed: reduce.threads=%d\n",
+         reduce_policy.multi_tile.threads_per_block);
+  return 0;
+}