Add CI workflow for Rust and TypeScript projects

[koteshyelamati]

What does this PR do?

Adds a GitHub Actions CI workflow (.github/workflows/ci.yml) that runs on every push and PR to main. Two parallel jobs:

1. Contract Tests (Rust) - installs stable Rust + wasm32-unknown-unknown target and runs cargo test --workspace inside contracts/ with Cargo caching.
2. Frontend Checks (TypeScript / pnpm) - sets up Node 20 + pnpm 9, installs deps, then runs:
   • pnpm -r typecheck (all packages)
   • pnpm --filter frontend lint
   • pnpm --filter frontend build

Both jobs use actions/cache for fast re-runs.

Which issue does this fix?

Closes #16

Checklist

• CI fails on broken test, type error, lint error, or build break
• Dependency caching included
• Follows conventional commits

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