Add keyboard-driven review workflow

[jzonthemtn]

Summary

For high-throughput document review, mouse-driven accept/reject/skip interactions are slow. Keyboard shortcuts would significantly improve reviewer efficiency.

Proposal

Add keyboard-driven workflow:

• Keyboard shortcuts for accept, reject, skip, and exempt actions
• Navigation shortcuts to move between entities and documents
• Configurable keybindings
• Display shortcut hints in the review UI

Acceptance Criteria

• All review actions (accept, override, exempt, skip, next, previous) mapped to keyboard shortcuts
• Shortcuts documented in the UI (help overlay or tooltip)
• Shortcuts do not conflict with browser defaults
• Reviewer can complete a full document review without using the mouse
• Tests cover shortcut functionality