macOS creates .DS_Store files in every folder which were being tracked
by git, causing constant conflicts when vaults are synced across machines.
init_repo() now writes a .gitignore before the first commit with:
- .DS_Store, .AppleDouble, .LSOverride
- ._ thumbnail files
- Common editor artifacts (.vscode/, .idea/, *.swp)
The file is only written if one doesn't already exist, so user-customized
.gitignore files are respected.
Two new Rust tests verify the behavior.
8712ce8e13