v2.21.31 — Windows Git Bash preflight for Codex validation

Summary

v2.21.31 adds a Windows PowerShell preflight for Codex plugin validation without creating a parallel PowerShell validator suite.

Added

• scripts/windows-preflight.ps1 checks codex, git, node, Git Bash, installed Codex plugin listing, and the common Windows collision where bare bash resolves to the WSL launcher without an installed distro.
• The preflight prints canonical Git Bash validator commands for PowerShell users.

Changed

• docs/codex-integration.md and docs/compatibility-matrix.md now state the Windows contract explicitly: Bash validators remain the single source of truth; Windows uses Git Bash as the compatibility layer.
• Release surfaces and the plugin/ child package mirror are bumped/synced to v2.21.31.

Validation

• Windows test station preflight on user01@10.100.94.171: 0 failures, 1 expected warning for WSL bash precedence.
• bash tests/validate-structure.sh: PASS 439, FAIL 0.
• bash tests/validate-content.sh: PASS 362, FAIL 0.
• bash tests/test-skill-graph.sh: PASS 78, FAIL 0.
• bash tests/test-verbosity-hook.sh: PASS 23, FAIL 0.
• PR #324 CI: validate, root linkcheck, and wiki linkcheck all passed.

Closes #323.