Sync client for docsgraph-server #2

Description

docsgraph needs to synchronize the local-first document store with a self-hosted docsgraph-server instance when connected, and keep working seamlessly when offline.

Proposed Solution

Implement a sync client that talks to docsgraph-server's sync protocol, handles authentication, and merges remote changes into the local store.

Acceptance Criteria

• Client can connect to a configured docsgraph-server instance
• Local changes push to the server and remote changes pull to the client
• Sync degrades gracefully when offline and resumes on reconnect
• Conflicts are surfaced or resolved according to the documented strategy