Change-stream split events + four cluster role bundles
Summary: Opt-in splitEvent envelope on every change-stream event and four documented mongod cluster role bundles — clusterMonitor, clusterAdmin, backup, restore — join the built-in role set (v0.3.0a76).
The splitLargeChangeStreamEvents option now stamps a splitEvent: {fragment: 1, of: 1} envelope on every change-stream event — insert, update, delete, replace, invalidate. Without the option the field stays absent, exactly as on mongod. SecantusDB's events never approach the 16MB BSON cap, so every fragment is a single, but drivers that lean on the envelope's presence (or asymmetric-write code paths that reassemble fragments unconditionally) now see what they expect.
Four cluster role bundles join the existing root / *AnyDatabase set in secantus.rbac.BUILT_IN_ROLES. clusterMonitor (read-only monitoring), clusterAdmin (monitoring + fsync + dropDatabase), backup (read every db + monitoring), restore (write every db + DDL + user/role management). All admin-bound, all span every database — the same shape mongod's documented privilege bundles ship. Backup tools and monitoring users get a proper bound role assignment instead of needing root.