feat(sound): add realistic 3D brake pad friction squeak sound on braking

[CanerKaraca23]

Summary

Adds an optional, realistic 3D positional brake pad friction squeak sound effect when braking on older, vintage, classic, high-mileage, budget, and commercial work vehicles.

Key Changes

• Brake Pad Physics & Acoustics:
  • Requires wheel ground contact (m_nWheelsOnGround > 0) so jumping/flying vehicles in mid-air do not trigger brake friction noise.
  • Checks foot brake pedal (m_fBreakPedal) and handbrake (bIsHandbrakeOn).
  • Implements an acoustic speed roll-off curve: sound intensity smoothly decays as the vehicle slows down to a stop ($< 6 \text{ km/h}$).
  • Smooth frame-to-frame volume interpolation (~150ms fade-out) eliminates abrupt audio cutoffs upon stopping.
• Curated 69-Vehicle Whitelist:
  • [TABLE] BrakePad_VehicleModels: Curated list of 69 vintage, 50s-70s classics, older 80s/90s budget sedans/coupes, and heavy-duty work vans/pickups.
  • Excludes modern supercars, pristine sports cars, luxury limousines, and serviced emergency fleets.
• Configuration:
  • [SOUND] BrakePadSound: Defaults to 0 (disabled by default).
  • [SOUND] BrakePadOnlySelected: Defaults to 1 (whitelisted models only).
  • Per-vehicle JSONC override support via "sound": { "brake_pad": true/false }.
• Audio Asset:
  • Added clean brake_pad.mp3 sound asset with all metadata tags stripped.
  • Supports custom .mp3, .wav, .ogg audio overrides.