Prepare ReproMin v0.1.0.dev13

[fly1d]

Why

The corrected Doctor readiness state on main is not in a release yet. The existing front door also hides reduction behind a positional SOURCE and makes users repeat the synthetic demo before reaching a real repository.

What changed

• Add an explicit repomin reduce command while preserving the original syntax.
• Replace the dense root help with a short task-oriented entry page and update all four shell completions.
• Route the README, English quick start, and Chinese quick start through a strict real-repository workflow: reproduce, Doctor, bounded reduction, validate, replay, then adopt the result.
• Keep the PowerShell guide as a clearly labeled runnable platform walkthrough.
• Test documented command order and contracts, plus real Doctor, reduction, validation, and replay JSON outcomes.
• Prepare version 0.1.0.dev13 and clarify command side effects and payload fingerprint guarantees.

Verification

• Contributor preflight: 775 tests passed, 4 platform-specific skips
• Offline benchmarks: 16 passed
• Documentation and quick-start checks passed
• Ruff and byte compilation passed
• Wheel and sdist build, twine, and structural validation passed
• Fresh isolated wheel and sdist installs each passed the quick start and all 775 tests

PYPI_PUBLISH_ENABLED remains false. This PR does not publish to PyPI or create a release tag.