feat(simulation): math, deterministic trig, RNG, clock, hasher (Phase 2, PR 3/5)

[CodeByBryant]

Summary

Phase 2, PR 3 of 5. The deterministic building blocks the world kernel (PR 4) is made of. No World behavior yet.

• Math: scalar (clamp, lerp, wrapAngle, PI constants), vector (add/sub/scale/dot/length/distance/normalize/clampLength/angle/fromAngle/lerp), geometry (rect containment, clamp to rect, circle containment/intersection, circle-rect). Pure functions, no Math.hypot.
• Deterministic trig (math/trig.ts): fdlibm ports of sin, cos, atan2, ln using only IEEE-exact operations. Domains are documented and enforced with RangeError.
• RNG: SeededRandom (xoshiro128**, float/integer/boolean/normal/choose, getState/setState including the cached normal spare), RandomStreams for the six named streams, and the exact derivation from the spec ("evo-rng-v1" bytes -> FNV-1a -> splitmix32 -> state, with the all-zero fallback).
• Clock: SimulationClock (fixed timestep, time = tick * deltaTime by multiplication, never accumulated).
• Hasher: StateHasher (cyrb128-style 128-bit, big-endian float64 bits, -0 canonicalized, throws on non-finite, versioned header via HASH_SCHEMA_VERSION), plus an exact utf8Encode (the engine cannot use TextEncoder).
• docs/simulation/determinism.md gains the normal() vectors and an accuracy statement.

Simulation impact

• Changes determinism (implements the accepted spec; ADR 0003)

Determinism

• Uses the seeded random source; no Math.random(), wall clock, platform transcendentals or ** (ESLint enforces it on this code)
• Determinism tests were added

Testing

Fresh clone: install --frozen-lockfile, format:check, check and build pass. 85 simulation tests (3 contracts, 24 config):

• Every vector in determinism.md section 10 is reproduced by the real implementation (xoshiro reference, splitmix32, FNV-1a, stream derivations, float(), all-zero fallback, hasher digests including -0 canonicalization). Two of them (xoshiro reference, FNV-1a of a) match published values, giving independent confirmation of the spec.
• sin/cos within 1e-15 of the platform over |x| <= 1e6 (including neighborhoods of multiples of pi/2), atan2 within 1e-15 (including wildly different magnitudes and signed zeros), ln within 2e-16 relative over 1e-300..1e300 and near 1.
• Stream isolation (drawing from world leaves environment and genetics untouched), save/restore continuing the exact sequence including a cached spare, chi-square uniformity of integer, normal mean/sigma/tails.

Review notes

• The fdlibm coefficients were entered from memory; the accuracy tests against the platform functions are what validate them (they passed first time), and the normal() vectors agree exactly with a Math.log reference.
• Trig accepts |x| <= 1,000,000 and throws beyond it (Payne-Hanek reduction is deliberately not implemented; the engine wraps angles).
• The placeholder World/ENGINE_VERSION in index.ts are untouched; PR 4 replaces them.

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