Bug: git worktree fails with 'branch already used' when parallel agents attempt same branch

Bug Description

When oh-my-claudecode orchestrates parallel tool calls (e.g., ultrawork mode), multiple agents may attempt to create git worktrees with the same branch name simultaneously, causing exit code 128 errors.

Error Output

Error: Sibling tool call errored
Error: Exit code 128
새로 만든 'bugfix/workflow-start-node-position' 브랜치로 전환합니다
작업 트리 준비 중 ('bugfix/workflow-start-node-position' 가져오중)
fatal: 'bugfix/workflow-start-node-position' is already used by worktree at '/Users/veluga/Documents/misc/veluga-frontend'

M  src/components/features/Pages/Workflow/components/builder/WorkflowBuilderInner.tsx
M  src/components/features/Pages/Workflow/components/panels/HttpRestNodeForm/index.tsx
M  src/components/features/Pages/Workflow/components/panels/PropertyPanel/NodePropertyForm.tsx

Expected Behavior

• Parallel agents should not collide on branch names when creating worktrees
• Each agent should use a unique branch name (e.g., append a suffix or agent ID)
• Or: agents should check if a worktree with that branch already exists before attempting to create one

Reproduction Steps

1. Activate ultrawork or parallel execution mode
2. Have multiple agents attempt to create worktrees for related bugfixes
3. If two agents pick the same branch name, one will fail with exit code 128

Environment

• oh-my-claudecode (latest)
• macOS
• Git worktree-based parallel execution

Suggested Fix

• Before git worktree add, check git worktree list for existing worktrees using the target branch
• If branch already in use, either reuse the existing worktree or append a unique suffix (e.g., -2, -agent-id)
• Handle the error gracefully instead of failing the entire sibling tool call