Incremental diff reviewer for DeepSeek Harness

Key features

• Incremental review (since-review): approving snapshots the working tree into a checkpoint
• the next review diffs checkpoint -> current, so reviewed files disappear from the queue unless they change again.
• Two entry pointsa Web UI review panel docked above the conversation composer (2s polling), and a /review command for keyboard-first use.
• The same core logic backs both.
• Feedback closed loopapprovals may carry a comment, delivered to the agent as a user message via agent.inject().