Add CI test pipeline

[bbethell-1]

Findings

No CI pipeline for code testing (High)

• .github/workflows/ contains only docs.yml. No workflow runs pytest, linting, or type checking on PRs.

Async tests missing pytest.mark.asyncio (Medium)

• src/api/tests/test_auth_middleware.py: All async test methods lack @pytest.mark.asyncio decorator. Tests may silently pass without executing async code.

test_streaming.py requires live Redis (Medium)

• src/api/tests/test_streaming.py line 53: test_relay_publishes_and_receives connects to redis://localhost:6379 directly, not marked as integration test.

Proposed Fix

• Add GitHub Actions workflow for pytest + type checking
• Add @pytest.mark.asyncio to async tests
• Mark Redis-dependent tests with @pytest.mark.integration

cc @stencell