Add CI workflow for typecheck and tests

[Bre77]

What

• Add a GitHub Actions workflow (.github/workflows/ci.yml) that runs on push to main and on every pull request:
  • Installs deps with pnpm install --frozen-lockfile.
  • Typechecks with tsc --noEmit.
  • Runs the vitest suite with pnpm test.
• The repo had no CI configured - PR Wire signed-command building/dispatch through a transport-agnostic Commands seam #5's signed-command layer added a full test suite and a tsc build gate, but nothing enforced either on PRs. This wires both in so the upcoming BLE/router work is gated on green CI instead of relying on local runs.