Add lightweight orchestrator CLI with supervisor/worker subprocess flows

[mmprotest]

Motivation

• Provide a dead-simple, deterministic orchestrator for multi-step repo work that reuses the existing CLI runner as subprocesses and keeps orchestration logic outside model output parsing.
• Keep the design minimal: supervisor + worker roles only, up to 3 subtasks, up to 1 retry per worker, and deterministic verification outside the model.

Description

• Added a new top-level CLI command orchestrate that invokes villani_code.orchestrator.run_orchestrator(...) and prints a concise final summary.
• Extended run in villani_code/cli.py with hidden machine-only flags --role, --result-json-path, and --parent-mission-id, and made run emit a strict JSON artifact to the provided --result-json-path when present while preserving normal UX.
• Implemented orchestrator modules: villani_code/orchestrator.py (controller + subprocess launcher), villani_code/orchestrator_models.py (typed dataclasses and state persistence), villani_code/orchestrator_roles.py (supervisor/worker prompt builders), villani_code/orchestrator_git.py (minimal git worktree/merge/diff helpers), and villani_code/orchestrator_verify.py (deterministic worker and final verification heuristics).
• Kept subprocess approach: the orchestrator runs child agents via python -m villani_code.cli run ... (see run_villani_subprocess) and consumes the strict JSON artifact at --result-json-path instead of parsing human stdout.
• Updated villani_code/subagent_runtime.py to include supervisor and worker role presets with simple allowed-tool constraints.
• Added focused tests under tests/ that mock subprocess/git interactions to validate direct/split supervisor behavior, invalid supervisor artifacts, retry/blocked/timeout flows, merge/final-verification failure handling, and CLI machine-artifact emission.

Testing

• Ran the new unit tests with: pytest -q tests/test_orchestrator.py tests/test_cli_orchestrator_flags.py and all tests passed (12 passed).
• Tests mock subprocess and git operations to avoid live model calls and real worktrees while exercising orchestrator logic and state persistence under .villani_code/missions/<mission_id>/orchestrator/.

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Codex Task