feat: add WASM support for browser-based proof generation

[Bisht13]

Summary

• Add wasm32 architecture support to Skyscraper field arithmetic
• Add WASM bindings for Prover and Verifier (provekit-wasm)
• Add Node.js and browser demo with noir_js integration

Changes

• skyscraper: wasm32 block multiplier, fp-rounding stubs, SIMD codegen
• provekit-wasm: Prover and Verifier classes with proveBytes() API
• playground/wasm-node-demo: Setup scripts, browser UI, Node.js CLI demo

Usage

cd playground/wasm-node-demo
pnpm install
pnpm run setup -- path/to/noir-circuit
pnpm run demo # Node.js
pnpm run demo:web # Browser (localhost:8080)

Blocked on #198