[codex] Add transactional agent runtime and Windows support

[wusuiling-if]

What changed

• add a framework-independent Git worktree transaction state machine with explicit prepare, authenticated receipt, conflict-checked commit, abort, resume, and status flows
• keep Agent tool auditing in a separate adapter so the transaction core does not import LangGraph or Agent contracts
• add platform-aware command execution, Windows process-tree cleanup, cross-platform file locks, and structured-file fallbacks
• exercise the native Windows runtime and both no-key demos in CI
• reposition the project documentation around transactional, verification-bound agent execution

Why

The project is narrowing its focus to one defensible mechanism: an agent should produce a verified, inspectable patch in isolation and must not mutate the source worktree until an explicit commit succeeds. The command runtime also assumed POSIX shell and locking APIs, which prevented native Windows execution.

Impact and limits

Native Windows now runs the Agent, structured tools, and transaction demos through cmd.exe. Windows has no built-in strong sandbox backend: --sandbox auto uses Docker when available, while --sandbox none remains an explicit unisolated opt-out. The Windows structured-file fallback cannot provide the same descriptor-relative race resistance as POSIX.

Validation

• pytest -q: 326 passed, 1 skipped
• offline verified-patch evaluation: 11/11 passed
• python -m pip check: no broken requirements
• mca demo: passed
• mca tx demo: successful commit plus concurrent-conflict refusal with the user change preserved