Add journal sync between Obsidian vault and server.
- Journal entries sync bidirectionally (pull from server, push local changes)
- Entries stored as markdown with YAML frontmatter in Logography/Journal/
- Vault wins on conflicts (newer modification time pushed to server)
- Manual sync only: use Command Palette > 'Sync Journal' or Settings > 'Sync journal' button
- No auto-sync on load