No FileVersion event pruning after supersede

[rita-aga]

Problem

When a FileVersion is superseded (e.g., agent rewrites an embodiment file), both the old and new version retain full event history. Old superseded versions accumulate events that serve no purpose.

Evidence (Katagami pipeline, 5-query run)

• 12,053 FileVersion.Create events (4.8MB)
• 10,417 FileVersion.Supersede events
• Embodiment files that go through multiple drafts (agent writes, compiles, rewrites) accumulate old version events

Impact

Minor storage impact today (4.8MB), but grows with pipeline throughput. Superseded versions are never cleaned up.