Bugbot adds PR review effort controls

This is a practical knob, not a flashy one, and that makes it more important: Cursor is turning code review quality into an explicit tradeoff between latency and bug yield.

• –High effort is the right default for high-risk code paths like infra and backend, where missed bugs are expensive
• –Custom effort is the more interesting piece because it makes review policy configurable in plain English, not just a binary toggle
• –The reported lift from 0.7 to 0.95 bugs per run suggests Cursor is pushing Bugbot toward a more selective but deeper reviewer
• –Usage-based billing gating the feature keeps it aligned with teams that already care about measurable review ROI
• –This strengthens Bugbot as a production code-review tool, not just an AI comment generator