Add dynamic memory-based asset caching and aggressive loading

- Add MemoryMonitor class for dynamic cache sizing based on available RAM
- Increase terrain load radius to 8 tiles (17x17 grid, 289 tiles)
- Scale worker threads to 75% of logical cores (no cap)
- Increase cache budget to 80% of available RAM, max file size to 50%
- Increase M2 render distance: 1200 units during taxi, 800 when >2000 instances
- Fix camera positioning during taxi flights (external follow mode)
- Add 2-second landing cooldown to prevent re-entering taxi mode on lag
- Update interval reduced to 33ms for faster streaming responsiveness

Optimized for high-memory systems while scaling gracefully to lower-end hardware.
Cache and render distances now fully utilize available VRAM on minimum spec GPUs.

include/game/game_handler.hpp

@@ -965,6 +965,7 @@ private:
     bool taxiActivatePending_ = false;
     float taxiActivateTimer_ = 0.0f;
     bool taxiClientActive_ = false;
+    float taxiLandingCooldown_ = 0.0f;  // Prevent re-entering taxi right after landing
     size_t taxiClientIndex_ = 0;
     std::vector<glm::vec3> taxiClientPath_;
     float taxiClientSpeed_ = 18.0f;  // Reduced from 32 to prevent loading hitches