[APIView] WI-16: GetReviewStatus & Copilot Trigger

## Goal

Make `GetReviewStatus` version-aware and implement version-level Copilot automation triggers.

**Area:** Approvals · **Depends on:** WI-3 · **Stable alone:** ✅ Yes — additive, backward-compatible

## Deliverables

### Update `GetReviewStatus` (release gating)

Update `AutoReviewController.GetReviewStatus`:
- **Before:** Iterates revisions to find matching `PackageVersion`, checks `IsApproved`
- **After:** `NormalizeVersion(packageVersion)` → look up `APIVersion` by `(reviewId, versionIdentifier)` → return `version.IsApproved`
- Backward compatible: if no matching `APIVersion` exists, fall through to revision-level check

### Update Copilot automation trigger

Per §7.2:
1. On version creation/new revision, check `APIVersionModel.IsReviewedByCopilot`
2. If `false` and `Kind = Stable` (or PR resolving to stable): enqueue Copilot review, set `IsReviewedByCopilot = true`
3. `Preview`/`RollingPrerelease`: skip automatic trigger
4. Manual Copilot requests tracked via `ReviewRequestIds`, don't set `IsReviewedByCopilot`

### Tests

- `ReviewsControllerTests.cs` — `GetReviewStatus` returns from version; backward-compatible fallback
- `CopilotTriggerTests.cs` — Stable triggers; preview doesn't; rolling prerelease doesn't; duplicate prevention

### Documentation

Update `docs/release_approval.md` §6: `GetReviewStatus` resolves by version.

Start with AutoReviewController.GetReviewStatus and the version models involved in the issue, then read ReviewsControllerTests.cs and CopilotTriggerTests.cs. Run the named tests to understand current revision fallback and trigger behavior. Done means version-aware status with fallback, correct Stable/Preview/RollingPrerelease and duplicate handling, passing tests, and the §6 update in docs/release_approval.md.

Written by the indexing model from the issue text.