wt add fails to install dependencies when virtual environment doesn't exist in new worktree

[notdp]

Environment

• OS: macOS (Darwin 24.6.0)
• worktree.sh version: latest from main branch

Steps to Reproduce

1. Initialize project configuration:

wt init

2. Configure install command as:

. ".venv/bin/activate" && pip install -r requirements.txt

3. Create a new worktree:

wt add feature-name

Actual Result

📦 Installing dependencies (. ".venv/bin/activate" && pip install -r requirements.txt)
sh: .venv/bin/activate: No such file or directory

Dependency installation fails because the .venv virtual environment doesn't exist in the new worktree directory.

Expected Result

The install command should execute successfully, or provide clear guidance when the virtual environment is missing.