.DS_Store should be filtered out in all directories (#61)

## Summary
**Issue**:  
The current `.gitignore` patterns are not effectively ignoring
`.DS_Store` files across the project.

- `**/.DS_Store/`: The trailing slash treats `.DS_Store` as a directory,
so it doesn’t match `.DS_Store` files as expected.
- `/frontend/.DS_Store`: This only ignores `.DS_Store` files in the root
of the `frontend` directory, not in its subdirectories.

**Solution**:  
Using `**/.DS_Store` will correctly ignore `.DS_Store` files in all
directories throughout the project, resolving both issues.

## Checklist
- [ ] Added Unit Tests
- [ ] Covered by existing CI
- [ ] Integration tested
- [ ] Documentation update



<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

- **Chores**
- Updated the `.gitignore` file to better reflect project structure by
adding and removing entries for ignored files and directories.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: ken-zlai

.gitignore

@@ -14,7 +14,7 @@
 .eclipse
 **/.vscode/
 **/__pycache__/
-**/.DS_Store/
+**/.DS_Store
 api/py/ai/chronon/api/
 api/py/test/sample/production/group_bys/quickstart/
 api/py/test/sample/production/joins/quickstart/
@@ -57,7 +57,6 @@ releases
 /frontend/build
 
 # Frontend OS
-/frontend/.DS_Store
 /frontend/Thumbs.db
 
 # Frontend Env