Fix bind mount failure when ~/.gitconfig does not exist (#24)

Docker bind mounts require the source file to exist. Users without
~/.gitconfig (fresh machines, XDG-based config, system-only config)
hit a container start failure.

Add initializeCommand to create an empty ~/.gitconfig on the host
before the container starts. An empty gitconfig is valid and has no
side effects — git treats it as having no settings.

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

devcontainer.json

@@ -63,6 +63,7 @@
     "PYTHONDONTWRITEBYTECODE": "1",
     "PIP_DISABLE_PIP_VERSION_CHECK": "1"
   },
+  "initializeCommand": "test -f \"$HOME/.gitconfig\" || touch \"$HOME/.gitconfig\"",
   "workspaceMount": "source=${localWorkspaceFolder},target=/workspace,type=bind,consistency=delegated",
   "workspaceFolder": "/workspace",
   "postCreateCommand": "uv run --no-project /opt/post_install.py"