Add R/WebAssembly

[bbbruce]

Summary

Adds R/rwasm to existing Python/Pyodide and Rust/WASM flows.

Changes

• Adds @cfasim-ui/rwasm runtime support for loading R models in the browser.
• Adds the shared cfasim R helper package for model output construction.
• Adds cfasim init --template R with a minimal R package model and interactive Vue app.
• Adds an R example to the models app with Playwright coverage.
• Adds R/rwasm docs.

Validation

• Pre-commit and vitest suite passed.
• Scaffold/render Playwright coverage passed locally.