feat: infinite terrain streaming with 3-chunk radius

[maxfelker]

Summary

Implements true infinite terrain — as the player walks, the world generates ahead of them with no visible edge.

Changes

Go / WASM

• RenderRadius: 512 → 1536 (3-chunk radius, ~28 chunks visible at once)
• DistanceThreshold: 1100 → 2560 (5-chunk eviction with hysteresis to prevent thrash)
• MaxConcurrentChunks: 3 → 64 (removes the throttle that limited initial load to 3 chunks)
• World.Update(): Stripped redundant heightmap/normals generation — goGenerateChunk owns that. Update is now pure coordinate math, returning sorted nearest-first chunk list
• Center-based distance: Uses chunk center (cx+0.5)*size instead of corner for more accurate circular loading
• goWorldUpdate: Only evicts heightmaps on chunk removal (generation side was already handled by goGenerateChunk)

TypeScript

• Parallel generation: streamUpdate now uses Promise.all — all new chunks in a batch are queued to the WASM worker concurrently (GPU upload happens progressively as each completes)
• Stream trigger: 256 → 128 units — fires every quarter-chunk of movement for more responsive horizon loading
• Immediate first stream: lastStreamX/Z initialized to -99999 so the render loop triggers a full streaming pass on the very first frame

Testing

• All Go tests pass
• All 56 TypeScript tests pass
• Docker production build passes (67MB image)

Reviewable commits

1. e4acee5 — Go world streaming: 3-chunk radius, no throttle, no redundant generation
2. 7d1ef58 — TypeScript: parallel chunk gen, faster stream trigger, immediate first stream