Claude Code 2.1.221: zsh permission bypass fixed, sandbox credential masking

Fixes a Bash permission-check bypass where zsh could execute hidden commands inside `[[ ]]` regex conditionals, plus a Windows PowerShell path-quoting mishandling in permission checks. Adds credential masking for sandboxed commands on Linux/WSL and changes `/fork` to create its own worktree.

Tool: claude-code · Version: 2.1.221 · Significance: 4/5 · security, fix, feature