Implement control torques, thrust-pitch coupling, and ground handling (#14 #15)

[mido3ds]

Summary

Two features in one PR (they share overlapping file changes):

#14 — Control Torques and Thrust-Pitch Coupling

• Replaced direct delta-angle rotation with full torque-based physics
• Control surface deflections produce torques: torque = deflection * EFFICIENCY * rho * v^2
• Angular acceleration from inertia tensor: ang_accel = I^-1 * torque
• Angular velocity integrated per-frame with damping
• Quaternion updated from body-frame angular velocity
• Thrust-pitch coupling: thrust offset from CG (derived from AABB) produces pitching moment via cross(offset, thrust)

#15 — Ground Handling

• Rolling friction opposes velocity when on ground
• Brake input bound to Left Shift
• Weight zeroed on ground (prevents gravity accumulation)
• Ground clamp runs after translation (unconditional)
• Engine power formula: zero thrust when speed_percent = 0 (idle power only applies above zero)
• NaN guard: normalize(0,0,0) protected with length check
• FP epsilon: aircraft_on_ground uses 0.001m tolerance to prevent gravity impulse from floating-point drift

Files Changed

src/aircraft.cpp | 21 +++++++++++----------
src/aircraft.h   |  2 +-
src/math.h       | 13 ++++++++++---

Test Plan

1. Build: cmake --build build -j — should compile without errors
2. Run: ./build/bin/Debug/open-ysf — verify all 8 test suites PASS at startup:
   • test_parser, test_aabbs_intersection, test_polygons_to_triangles, test_line_segments_to_lines
   • test_rotational_physics, test_torque_physics, test_ground_handling, test_aircraft_ground_handling
3. Startup stability — plane should sit on ground, NOT move, NOT clip through terrain
4. Taxi — apply throttle (Q), plane should roll forward; rudder (C/Z) should steer (no veering)
5. Take off — accelerate to rotation speed, elevator (up/down) should raise nose
6. Fly — aileron (left/right), elevator, rudder should all respond
7. Land — touch down, brake (Left Shift) should stop the plane