Add `--dry` mode

Sometimes you don't want to update files just yet. You might want to see what files will change (both locally and remotely) and the diff for them, and only after that confirm pulling or pushing updates.

Start by locating the CLI argument handling and the synchronization flow for local and remote updates. Trace how pulling and pushing currently change files, then define dry mode as a preview of affected files and their diffs without applying changes, followed by confirmation before updates proceed.

Written by the indexing model from the issue text.