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.

engines/saab-expansion.toml

@@ -0,0 +1,152 @@
+# Engine definition. Dimensional keys state their units.
+schema_version = 1
+id = "saab-expansion"
+name = "Saab B205 / expansion silencers"
+category = "Inline four / Saab"
+description = "Two single expansion chambers, same body volumes"
+order = 5
+cycle = "four_stroke"
+
+[engine]
+bank_angle_deg = 56.0
+collector_volume_litres = 0.6
+cylinders = 4
+initial_rpm = 1200.0
+initialize_phased_charge = true
+layout = "inline"
+maximum_load_torque_nm = 200.0
+minimum_substeps = 2
+phase_degrees = [0.0, 180.0, 540.0, 360.0]
+pipe_damping = 0.0
+plenum_volume_litres = 3.0
+starter_torque_nm = 65.0
+throttle_diameter_mm = 52.0
+topology = "collector"
+
+[cylinder]
+afr = 14.7
+ambient_temperature_k = 300.0
+bore_mm = 90.0
+burn_duration_deg = 60.0
+burn_start_deg = 5.0
+compression = 8.8
+energy_variation = 0.05
+exhaust_close_deg = 390.0
+exhaust_open_deg = 130.0
+exhaust_valve_count = 2
+exhaust_valve_diameter_mm = 28.0
+exhaust_valve_lift_mm = 8.0
+fuel_lhv_j_per_kg = 4.4e+07
+heat_transfer = 100.0
+intake_close_deg = 590.0
+intake_open_deg = 340.0
+intake_valve_count = 2
+intake_valve_diameter_mm = 32.0
+intake_valve_lift_mm = 8.5
+misfire_probability = 0.0
+rod_mm = 153.0
+stroke_mm = 78.0
+wall_area = 0.02
+wiebe_a = 5.0
+wiebe_m = 2.0
+
+[crankshaft]
+friction_constant_nm = 12.0
+friction_quadratic_nm_s2 = 0.0
+friction_viscous_nm_s = 0.012
+inertia_kg_m2 = 0.18
+
+[ecu]
+idle_base_opening = 0.08
+idle_control = "feedback"
+idle_ki = 4e-05
+idle_kp = 0.0001
+idle_max_opening = 0.25
+idle_minimum_advance_deg = -10.0
+idle_rpm = 850.0
+idle_spark_gain = 0.025
+ignition_map = [[0.0, 10.0], [15000.0, 40.0]]
+overrun_cut_rpm = 2000.0
+overrun_fuel_cut_enabled = true
+overrun_ignition_cut_enabled = false
+overrun_resume_rpm = 1300.0
+power_afr = 12.8
+rev_limit_enabled = true
+rev_limit_fuel_cut_enabled = true
+rev_limit_rpm = 6500.0
+rev_resume_rpm = 6250.0
+stoichiometric_afr = 14.7
+throttle_closing_rate = 0.0
+throttle_closing_time_constant_s = 0.0
+throttle_rate = 1000.0
+throttle_time_constant_s = 0.001
+
+[vehicle]
+air_density = 1.225
+clutch_capacity = 300.0
+clutch_engagement_rate = 8.0
+drag_coefficient = 0.32
+final_drive_ratio = 4.05
+frontal_area = 2.2
+gear_ratios = [3.382716, 1.758025, 1.177778, 0.8938271, 0.6592593]
+gravity = 9.80665
+mass_kg = 1675.0
+primary_reduction = 1.0
+rolling_resistance = 0.015
+rotational_inertia_kg_m2 = 3.6
+wheel_radius_mm = 317.0
+
+[fuel]
+system = "injection"
+
+[silencers]
+cell_length_mm = 35.0
+connecting_length_mm = 800.0
+diameter_mm = 60.0
+enabled = true
+inlet_length_mm = 1400.0
+outlet_length_mm = 350.0
+
+[silencers.resonator]
+chambers = 1
+core_diameter_mm = 60.0
+length_mm = 400.0
+loss_coefficient = 0.1
+passage_diameter_mm = 60.0
+resistance = 2.0
+type = "expansion"
+volume_litres = 6.0
+
+[silencers.muffler]
+chambers = 1
+core_diameter_mm = 60.0
+length_mm = 650.0
+loss_coefficient = 0.35
+passage_diameter_mm = 60.0
+resistance = 4.0
+type = "expansion"
+volume_litres = 18.0
+
+[[pipes]]
+id = "intake"
+cells = 8
+diameter_mm = 60.0
+length_mm = 150.0
+
+[[pipes]]
+id = "runners"
+count = 4
+cells = 10
+diameter_mm = 32.0
+length_mm = 250.0
+
+[[pipes]]
+id = "primaries"
+count = 4
+cells = 10
+diameter_mm = 34.0
+length_mm = 280.0
+
+[[pipes]]
+id = "tailpipe"
+profile = "silenced"