…ults

Adds a standalone WebGPU micro-benchmark page comparing three BN254
Montgomery product implementations for chained-mul throughput:

- cios (u32): mitschabaude runtime-loop CIOS over 20×13-bit limbs.
  Baseline, ~109 ms at n=2^20, k=100.
- karat (u32): recursive Karatsuba + Yuval reduction. 9 5×5 schoolbook
  sub-sub-products are computed independently and combined via two
  Karatsuba levels; reduction uses precomputed r_inv = W^-1 mod p with
  zero drains in the multiply phase (unsigned wrap unwinds via
  subsequent subtraction). ~80 ms (~28% faster than cios).
- sos3uv3 (f32, reference): 22-bit f32 limbs with separate per-slot
  tlo/thi accumulators that break the inner-j carry chain. Single
  drain per outer iter via bias_split_f32_le4w. ~79 ms.

The bench harness:
- bench-field-mul.html is a standalone page; reads ?path=u32|f32
  &n=N&k=K&validate-n=N&reps=R&variant=V from the URL.
- bench-field-mul.ts runs k chained Mont mults per thread, validates
  the first `validate-n` outputs against a host BigInt reference, and
  writes timing into window.__bench.
- scripts/bench-field-mul.mjs is a Playwright driver for headless
  invocation from the CLI (added playwright-core as devDependency).

Routes the `montgomery_product_funcs` mustache partial through a
pre-rendered Karatsuba+Yuval body in every MSM shader that does a
base-field multiply (15 callsites: convert_points, smvp, horner,
batch_affine_{apply,schedule,finalize_*,init,apply_scatter},
batch_inverse{,_parallel}, bpr, decompress_g1, montgomery_parity).

The Karatsuba body benches ~27% faster than the mitschabaude
runtime-loop CIOS at n=2^20, k=100 (80 ms vs 109 ms). It exposes the
same `fn montgomery_product(x, y) -> BigInt` symbol plus the same
`get_p` / `conditional_reduce` helpers and uses the same 20×13-bit
limb layout, so the swap is a drop-in change with no callsite churn.

The field-mul bench retains both options (`?variant=cios` renders the
original template inline, `?variant=karat` reuses the class-level
default) so the two bodies can be compared side-by-side.