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, 3 insertions, 1 deletions

diff --git a/internal/config/config.go b/internal/config/config.go
index 91c107a..0fe1ac8 100644
--- a/internal/config/config.go
+++ b/internal/config/config.go
@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
+	"strings"
 )
 
 // Organization represents a git organization with its host and name
@@ -59,7 +60,8 @@ func (c *Config) Validate() error {
 		if org.Host == "" {
 			return fmt.Errorf("organization %d: missing host", i)
 		}
-		if org.Name == "" {
+		// Name can be empty for file:// URLs
+		if org.Name == "" && !strings.HasPrefix(org.Host, "file://") {
 			return fmt.Errorf("organization %d: missing name", i)
 		}
 	}