Add CI/CD workflow for Rust and WASM

[jbdevprimary]

Summary

Add GitHub Actions workflow for continuous integration.

Required Workflows

rust.yml

name: Rust CI
on: [push, pull_request]
jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: dtolnay/rust-toolchain@stable
        with:
          targets: wasm32-unknown-unknown
      - run: cargo check --all
      - run: cargo test --all
      - run: cargo clippy -- -D warnings
      - run: cargo fmt --check
      
  wasm:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: dtolnay/rust-toolchain@stable
        with:
          targets: wasm32-unknown-unknown
      - run: cargo install trunk
      - run: cd game-frontend && trunk build --release

Acceptance Criteria

• CI runs on all pushes and PRs
• Native and WASM builds pass
• Clippy and format checks pass