Part of #3277. Depends on the `py` script type foundation. **Why:** The smallest self-contained command that exercises git lookup, path resolution, file checks, and both JSON + text output — ideal to prove the pattern. ## Tasks - Implement `scripts/python/check_prerequisites.py` replicating all flags: `--json`, `--paths-only`, `--require-tasks`, `--include-tasks`, `--help`. - Port the needed `common.sh` / `common.ps1` helpers (feature-path resolution, branch detection) into a shared Python module. - Replace `jq` logic with stdlib `json`. ## Acceptance - Golden-output tests assert normalized parity between `.sh`, `.ps1`, and `.py` for each flag combination on a fixture repo.