feat: scaffold FCES-native C++ project with libtorch integration

- CMakeLists.txt with libtorch, GoogleTest, GoogleBenchmark, OpenMP, pybind11
- Header files: config, controller, population, fitness, evolution, spectral, oscillation, telemetry, optimizer
- Source implementations: controller (full micro-MLP forward pass, mutation, crossover), fitness (Welford's algorithm), oscillation (DFT), spectral (SVD rank), optimizer (sign-SGD stub)
- Tests: controller, population, fitness, optimizer (Google Test)
- Benchmarks: evolve throughput, optimizer step (Google Benchmark)
- Examples: simple optimization, PyTorch/libtorch integration
- Python extension: pybind11 bindings with setup.py
- README with architecture diagram and build instructions

include/fces/oscillation.hpp

@@ -0,0 +1,29 @@
+#pragma once
+
+/**
+ * @file oscillation.hpp
+ * @brief FFT-based oscillation detection (Phase 25).
+ */
+
+#include <vector>
+
+namespace fces {
+
+class OscillationDetector {
+public:
+    static constexpr int WINDOW_SIZE = 64;
+    static constexpr float POWER_THRESHOLD = 0.5f;
+
+    void update(float loss);
+    bool detect() const;
+    float get_score() const;
+    float get_variance_50() const;
+    void reset();
+
+private:
+    std::vector<float> loss_history_;
+    static std::vector<float> detrend(const std::vector<float>& signal);
+    static std::vector<float> compute_power_spectrum(const std::vector<float>& signal);
+};
+
+}  // namespace fces