[codex] fix poetry worktree environment setup

[m24927605]

Summary

Fix AIT attempt workspace provisioning for Python/Poetry projects that use local relative path dependencies.

The root cause was that AIT creates attempt worktrees under .ait/workspaces/<attempt>, so Poetry dependencies like ../repo-b no longer resolve to the original sibling repository layout. The new provisioning step detects Poetry local path dependencies after git worktree add, repairs valid source-layout paths with AIT-owned symlinks, creates a worktree-local Poetry virtualenv, and writes VS Code interpreter settings that point at the usable environment.

Changes

• Add Python/Poetry environment provisioning for attempt worktrees.
• Repair valid relative Poetry path dependencies without editing pyproject.toml.
• Run poetry check and poetry install during workspace setup.
• Write worktree-local .vscode/settings.json with python.defaultInterpreterPath.
• Exclude .venv/, .vscode/, and poetry.toml from the worktree Git index via local excludes.
• Record AIT-created symlinks in metadata and clean them up when the workspace is removed.
• Add regression tests for sibling path dependency resolution, interpreter detection, local ignores, cleanup, and missing path dependency failure.

Validation

• PYTHONPATH=src python3.14 tests/test_workspace.py
• PYTHONPATH=src python3.14 tests/test_app_flow.py
• PYTHONPATH=src python3.14 -m compileall -q src/ait/python_env.py src/ait/workspace.py

Deploy

No docs or package release files changed. This branch does not trigger the GitHub Pages deploy workflow; deployment will occur through the normal main-branch workflow after merge if applicable.