v0.2.0-pre.7 — cross-join + vault snapshots

Pre-release on npm `@next`. Lockstep bump of all 66 packages 0.2.0-pre.6 → 0.2.0-pre.7.

Highlights

• Cross-join query primitive (#277) — `.crossJoin(target, { as })` on `Query`. Cartesian + lateral, composes with `.where()` / `.groupBy()` / `.aggregate()`, cost-ceiling guarded (`CrossJoinTooLargeError`). Dim 11 v3.
• Vault snapshots (#279) — opt-in `withSnapshots()`: `db.snapshot()` / `db.listSnapshots()` / `db.restoreSnapshot()` with declarative retention + `ledgerHead` tamper-detection on restore.

Also

• CI de-flake of the cross-tab conflict test (#228c).
• Docs: subsystem pages + index rows for both features; hub CHANGELOG `0.2.0-pre.7`.

```
npm install @noy-db/hub@next
```