feat: Add comprehensive profiling system with F3 overlay

Add real-time performance profiling infrastructure to monitor frame times,
render performance, and identify bottlenecks.

Features:
- Profiler.h: ScopedTimer RAII helper for automatic timing measurements
- ProfilerOverlay: F3-togglable overlay displaying real-time metrics
- Detailed timing breakdowns: grid rendering, entity rendering, FOV,
  Python callbacks, and animation updates
- Per-frame counters: cells rendered, entities rendered, draw calls
- Performance color coding: green (<16ms), yellow (<33ms), red (>33ms)
- Benchmark suite: static grid and moving entities performance tests

Integration:
- GameEngine: Integrated profiler overlay with F3 toggle
- UIGrid: Added timing instrumentation for grid and entity rendering
- Metrics tracked in ProfilingMetrics struct with 60-frame averaging

Usage:
- Press F3 in-game to toggle profiler overlay
- Run benchmarks with tests/benchmark_*.py scripts
- ScopedTimer automatically measures code block execution time

This addresses issue #104 (Basic profiling/metrics).

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/Profiler.h

@@ -0,0 +1,111 @@
+#pragma once
+
+#include <chrono>
+#include <string>
+#include <vector>
+#include <fstream>
+
+/**
+ * @brief Simple RAII-based profiling timer for measuring code execution time
+ *
+ * Usage:
+ *   float timing = 0.0f;
+ *   {
+ *       ScopedTimer timer(timing);
+ *       // ... code to profile ...
+ *   } // timing now contains elapsed milliseconds
+ */
+class ScopedTimer {
+private:
+    std::chrono::high_resolution_clock::time_point start;
+    float& target_ms;
+
+public:
+    /**
+     * @brief Construct a new Scoped Timer and start timing
+     * @param target Reference to float that will receive elapsed time in milliseconds
+     */
+    explicit ScopedTimer(float& target)
+        : target_ms(target)
+    {
+        start = std::chrono::high_resolution_clock::now();
+    }
+
+    /**
+     * @brief Destructor automatically records elapsed time
+     */
+    ~ScopedTimer() {
+        auto end = std::chrono::high_resolution_clock::now();
+        target_ms = std::chrono::duration<float, std::milli>(end - start).count();
+    }
+
+    // Prevent copying
+    ScopedTimer(const ScopedTimer&) = delete;
+    ScopedTimer& operator=(const ScopedTimer&) = delete;
+};
+
+/**
+ * @brief Accumulating timer that adds elapsed time to existing value
+ *
+ * Useful for measuring total time across multiple calls in a single frame
+ */
+class AccumulatingTimer {
+private:
+    std::chrono::high_resolution_clock::time_point start;
+    float& target_ms;
+
+public:
+    explicit AccumulatingTimer(float& target)
+        : target_ms(target)
+    {
+        start = std::chrono::high_resolution_clock::now();
+    }
+
+    ~AccumulatingTimer() {
+        auto end = std::chrono::high_resolution_clock::now();
+        target_ms += std::chrono::duration<float, std::milli>(end - start).count();
+    }
+
+    AccumulatingTimer(const AccumulatingTimer&) = delete;
+    AccumulatingTimer& operator=(const AccumulatingTimer&) = delete;
+};
+
+/**
+ * @brief CSV profiling data logger for batch analysis
+ *
+ * Writes profiling data to CSV file for later analysis with Python/pandas/Excel
+ */
+class ProfilingLogger {
+private:
+    std::ofstream file;
+    bool headers_written;
+    std::vector<std::string> column_names;
+
+public:
+    ProfilingLogger();
+    ~ProfilingLogger();
+
+    /**
+     * @brief Open a CSV file for writing profiling data
+     * @param filename Path to CSV file
+     * @param columns Column names for the CSV header
+     * @return true if file opened successfully
+     */
+    bool open(const std::string& filename, const std::vector<std::string>& columns);
+
+    /**
+     * @brief Write a row of profiling data
+     * @param values Data values (must match column count)
+     */
+    void writeRow(const std::vector<float>& values);
+
+    /**
+     * @brief Close the file and flush data
+     */
+    void close();
+
+    /**
+     * @brief Check if logger is ready to write
+     */
+    bool isOpen() const { return file.is_open(); }
+};