feat(snowy-village): add Snowbound Crossing

[hoainho]

Summary

• Demo id / title: snowy-village / Snowbound Crossing — Mini Game
• Migrates the playable winter village into the current lazy-loaded catalog with the original scene models, animations, snowfall, smoke, fire, day/night controls, and gate interaction. The fixed gate frame stays collidable while the two leaves open.
• Runtime mesh labels use procedural-img2threejs_mesh_* except the two requested IDs, which remain exactly hyper3d_mesh_297a4bb9-ceab-4c9f-940d-fd78631b1cec:0 and hyper3d_mesh_f5ae0d3a-9839-44ac-a100-c4761df806a5:0.
• Hyper3D provenance remains in Snowy metadata. Other demos and shared sponsor content are unchanged.

Performance root cause and fix

• Chrome CPU profiles showed the snowfall update repeatedly raycasting flakes against every triangle in the house mesh: the baseline profile sampled intersectTriangle for 1.15 s and getVertexPosition for 0.71 s over 3.04 s. The particles do not cast shadows; their house collision raycasts were the CPU hotspot.
• Added a per-house BVH with first-hit-only exact raycasts. It preserves the original triangle intersections and snow effect while removing the repeated full-geometry traversal.
• The sun shadow map was 4096x4096 over a 320-unit light-space box (about 7.8 cm per texel). It is now 2048x2048 over ±16 units with a tighter far plane; this uses 4x fewer shadow texels and about 5x denser world-space shadow coverage, reducing shimmer without changing shadow casters; the separate daytime-lighting retune is documented below.

Verification

• At commit a0163aa, a clean-clone npm run build passed. The current follow-up passes npx tsc --noEmit, but this worktree Vite build fails with ENOENT while statting public/baseline/girl-character.glb (listed as 0 B here). Donate and iPhone Duo integrity checks pass.
• Browser production preview loaded the role assets, rendered the scene, and opened the gate with E; no page errors.
• After-fix production movement sample: 120 frames, mean 13.34 ms, p95 14.9 ms, max 15.3 ms, zero frames above 33 ms. Main-thread TaskDuration increased 0.418 s over 1.97 s; BVH raycast sample was 2.4 ms. The before/after profile removes the former triangle-intersection hot path.
• Prewarm smoke passed: nine core roles, 957 decoded images, campfire failure isolation/retry, and both mesh-name exceptions.

Contributor checklist

• Reference-image rights: overview image carried from the Snowy source project; an explicit license statement is not recorded.
• Generated via the img2threejs skill (version not recorded in source; Snowy provenance names Hyper3D).
• npm run build passes locally in a clean clone.
• Rendered-browser screenshot attachment; overview image is linked below, but no separate browser capture is uploaded.
• Only touched the demo folder, reference image, and registry; this PR also changes shared Viewer camera-orbit plumbing and Snowy control styling to preserve the authored interaction.
• Registry entry is complete and status is final.

Screenshot

Snowy Village overview image

One incidental case-insensitive triPo substring remains only inside the opaque base64 PNG payload in native/data/gate.mjs. The image bytes and hash are unchanged; there is no Tripo metadata, node label, or provenance in the Snowy feature.

Gate collision and daylight follow-up

• Open passage is measured in normalized gate-local coordinates from both hinges and the panel seam. The entire player collision box plus a 4 cm clearance must fit before only the gate-frame and leaf colliders are bypassed; other scene colliders remain solid.
• Live noon smoke: the player crossed the fully open gate from interior to exterior; approaches at both posts (z=1.998 and z=3.548) remained blocked at x≈-4.715. After closing, both leaves returned to approximately 0 radians and a 2 s outward movement attempt from x=-2.39 was blocked. Browser error capture was empty.
• Daylight is softer and warmer: hemisphere intensity 1.05→0.62, sun 1.65→1.15, environment intensity 0.82→0.40; SUN_DAY is #FFD796 and the directional-light target is at the house center. The noon browser capture retains roof/snow detail and warmer wood tones.
• npx tsc --noEmit and git diff --check passed.