Ignore macOS .DS_Store metadata files #84

Summary

macOS Finder metadata files are not ignored, making .DS_Store files appear as untracked repository changes.

Current behavior

Finder has produced untracked .DS_Store files at the repository root and under crates/. The root ignore rules do not exclude them, so they add noise to status output and can be committed accidentally.

Expected behavior

Platform metadata files should not appear in repository status or be eligible for accidental commits.

Suggested implementation

Add .DS_Store to the root .gitignore, which will cover the repository recursively, and remove any tracked instances if they are introduced.

Relevant files

• .DS_Store
• crates/.DS_Store
• crates/walgit-server/.DS_Store