Add a standalone Profiler module (S3.profiler.json, disabled by default)
that hosts the in-game frame-time overlay previously owned by Physics
Optimizer. The overlay now adapts to whichever modules are enabled:
- Always shows: render + physics frame-time graph, timing report.
- Physics Optimizer section (if enabled): LOD fast-path and auto-freeze
quick-toggles with live stats, debug car count line.
- Mesh LOD section (if enabled): total tracked cars, loco/freight split,
per-LOD-level counts refreshed once per second.
PhysicsOptimizerModule retains only the Harmony patches and
CarDebugVisualizer; ShowOverlay/OverlayOpacity removed from PhysicsSettings.
MeshLodInjector gains GetLodStats() and GetLodLevel() for the overlay.
BBox material shader search now tries URP/Lit before Standard.
/rpf overlay toggle redirected to ProfilerOverlayGUI.Instance.
