(orchestration): Track bypass events for automated review gates

## Component

API or orchestration

## Describe the feature

When repos enable automated pre-human review, record **break-glass bypass** events when a human or policy override merges or advances a PR without automated approval. Feed counts into evaluation dashboards to tune reviewer strictness.

## Use case

Automated reviewers only improve if operators measure when humans **disagree** with them. Without bypass telemetry, teams over-tighten or under-tighten rules based on anecdotes.

## Proposed solution

1. GitHub webhook handler detects merge/approve without required check (when check integration exists) or manual CLI `bgagent review bypass --reason`.
2. Persist `review_bypass` events with reason, actor, finding IDs dismissed.
3. Surface in `bgagent stats` and roadmap analytics widgets.

## Other information

- Depends on **feature-pre-human-automated-review-gate** or customer branch protection wiring; can ship CLI-only bypass logging first.
- Privacy: store finding categories, not full diffs, in event payload.

## Acknowledgements

- [ ] I may be able to implement this feature
- [ ] This might be a breaking change

## Acceptance criteria

- [ ] Bypass events written to `TaskEvents` with structured schema.
- [ ] Operator can list bypasses per repo for a time window via API or CLI.
- [ ] Documentation explains how bypass rate should influence policy tuning.
- [ ] Tests cover webhook and CLI bypass paths.

Start with the GitHub webhook handler, the manual bgagent review bypass command, and the TaskEvents schema mentioned in the issue. Trace how events reach bgagent stats and roadmap analytics widgets, then review existing webhook and CLI tests. Done means structured bypass events can be recorded and listed by repository and time window, with coverage for both paths and documentation for policy tuning.

Written by the indexing model from the issue text.