Add repository synchronization functionality

- Create sync package to handle git repository synchronization
- Implement multi-organization sync with branch tracking
- Add merge conflict detection and error handling
- Support cloning, fetching, merging, and pushing across all remotes
- Add --sync flag to synchronize repositories
- Add --work-dir flag for working directory specification
- Create test infrastructure with setup and conflict test scripts
- Update config validation to support file:// URLs
- Add comprehensive .gitignore entries for test artifacts

The sync package automatically:
- Clones repositories if not present
- Fetches updates from all configured organizations
- Merges changes from all remotes for each branch
- Pushes synchronized changes to all organizations
- Detects and reports merge conflicts for manual resolution

Test with: ./test/setup_test_repos.sh && ./gitsyncer --config test/test-config.json --sync test-repo

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

1 files changed, 7 insertions, 1 deletions

diff --git a/.gitignore b/.gitignore
index 7101fd7..9edbe9b 100644
--- a/.gitignore
+++ b/.gitignore
@@ -36,4 +36,10 @@ go.work.sum
 
 # OS files
 .DS_Store
-Thumbs.db
\ No newline at end of file
+Thumbs.db
+
+# Test artifacts
+test/work/
+test/work-*/
+test/repos/
+.gitsyncer-work/
\ No newline at end of file