Load engines from TOML and improve scenario audio and carb tuning

Migrate 32 engine definitions into validated startup-loaded TOML files and separate configuration and snapshots from scenario assembly. Add camera-based stereo propagation from shared pipe geometry, preserve exhaust character, tune carburetor mixtures and idle, use ignition cuts for carb engines, and support returning to the scenario menu.

Validation: full Windows build and all 14 CTest checks passed.

include/FluidSim/Engine.hpp

@@ -10,12 +10,16 @@ namespace fluidsim::port {
 
 class Ecu;
 
-class Crankshaft {
-public:
-    float omega{400.0f * 2.0f * pi / 60.0f};
-    float angle{}, previous_angle{}, inertia{0.2f};
+struct CrankshaftConfig {
+    float inertia{0.2f};
     float friction_constant{}, friction_viscous{};
     float friction_quadratic{}; // Nm / (rad/s)^2, dissipative windage term
+};
+
+class Crankshaft : public CrankshaftConfig {
+public:
+    float omega{400.0f * 2.0f * pi / 60.0f};
+    float angle{}, previous_angle{};
     float load_torque{}, drivetrain_torque{};
     float average_power{}, average_torque{};
 
@@ -28,18 +32,22 @@ private:
     float power_sum_{}, torque_sum_{};
 };
 
-class EngineCylinder : public Component {
-public:
-    Ecu* ecu{}; // Optional ideal electronic fuel/ignition controller.
-    bool transported_fuel{}; // Upstream carb meters the fuel species.
+struct CylinderConfig {
+    float intake_open{340}, intake_close{590}, exhaust_open{130}, exhaust_close{390};
     float bore{0.075f}, stroke{0.068f}, rod{0.112f}, compression{11.5f};
     float intake_valve_diameter{0.030f}, exhaust_valve_diameter{0.028f};
     int intake_valve_count{1}, exhaust_valve_count{1};
     float intake_valve_lift{0.005f}, exhaust_valve_lift{0.005f};
-    float phase{};
     float spark_advance{20.0f}, wiebe_a{5.0f}, wiebe_m{2.0f}, burn_duration{60.0f}, burn_start{5.0f};
     float afr{14.7f}, fuel_lhv{44.0e6f}, energy_variation{0.05f}, misfire_probability{};
     float wall_area{0.02f}, heat_transfer{100.0f}, ambient_temperature{300.0f};
+};
+
+class EngineCylinder : public Component, public CylinderConfig {
+public:
+    Ecu* ecu{};
+    bool transported_fuel{};
+    float phase{};
     bool rev_limit_enabled{};
     float rev_limit_rpm{7500.0f}, rev_limit_cut_time{0.05f}, rev_limit_hysteresis{200.0f};
     float air_mass{}, exhaust_mass{}, energy{}, volume{}, pressure{101325.0f};
@@ -78,7 +86,6 @@ protected:
 
 class FourStrokeCylinder final : public EngineCylinder {
 public:
-    float intake_open{340.0f}, intake_close{590.0f}, exhaust_open{130.0f}, exhaust_close{390.0f};
     float valve_area(float cycle_degrees, bool inlet) const override;
     void pre_step(Crankshaft& crank, float dt, float throttle) override;
 };