TradingCodex 0.1.0a3

Alpha release focused on Codex workspace setup reliability.\n\n- Clarifies README quick start so Codex agents use the virtualenv-local tcx command without relying on shell PATH.\n- Adds GitHub URL install guidance.\n- Keeps manual-only PyPI publication through the Release workflow.\n\nSmoke checks passed for PyPI install, workspace init, and ./tcx doctor.