rendering: weapon VFX full package — particle smoke, muzzle particles, tracers, shell physics

[shadow-kernel]

Context

The v2.7 weapon sample ships with 'lite' VFX (billboard flash + light pulse + pooled shell prefabs) because the GPU particle system doesn't exist yet. Once v3.3 lands particles, decals and soft particles, the weapon feel gets its full upgrade — this issue closes the loop the user asked for: smoke, particles, recoil, all 100% smooth.

Goal

Upgrade the template weapon to the full VFX stack: particle-based muzzle flash + lingering smoke (lit, soft particles), bullet tracers (beam renderer), impact particles + surface decals from the decal system, and shells with proper physics bounce + rest (Jolt if available, else depth collision).

Acceptance Criteria

• Muzzle: layered particle flash (2–3 frames) + smoke puff with soft-particle depth fade, spawned at the muzzle socket via .vfx asset
• Lingering barrel smoke after sustained fire (emission rate driven by script heat value)
• Tracer beams for every Nth shot via trail/beam renderer
• Impacts: surface-type particle burst + projected decal (blood/wood/plaster from the decal system)
• Shell casings collide and settle (physics or depth-collision fallback), pooled, capped
• Volumetric fog interaction: muzzle flash light pulse visibly scatters in foggy corridors
• Frame budget: full auto fire adds ≤ 1.0 ms GPU at 1440p on the reference GPU (profiler numbers in PR)

Technical Notes

All effects authored as .vfx assets + template scripts — engine stays generic. Socket spawn points come from GetBoneWorldTransform; the animation-event wiring from the v2.7 sample stays unchanged (events just point at richer effects).

Dependencies

• rendering: GPU particle system core + editor: Particle Editor window + rendering: decal system + rendering: trail & beam renderers
• templates: weapon sample (v2.7 baseline)